Import tzdata 2021bvendor/tzdata/tzdata2021b

20 files changed, 1092 insertions, 572 deletions

diff --git a/CONTRIBUTING b/CONTRIBUTING
index 01336fce7f74..537335423ff4 100644
--- a/CONTRIBUTING
+++ b/CONTRIBUTING
@@ -26,8 +26,11 @@ to work well.  Additions to data should contain commentary citing
 reliable sources as justification.  Citations should use https: URLs
 if available.
 
+For changes that fix sensitive security-related bugs, please see the
+file SECURITY.
+
 Please submit changes against either the latest release in
-<https://www.iana.org/time-zones> or the master branch of the development
+<https://www.iana.org/time-zones> or the main branch of the development
 repository.  The latter is preferred.  If you use Git the following
 workflow may be helpful:
 
@@ -36,9 +39,9 @@ workflow may be helpful:
       git clone https://github.com/eggert/tz.git
       cd tz
 
-  * Get current with the master branch.
+  * Get current with the main branch.
 
-      git checkout master
+      git checkout main
       git pull
 
   * Switch to a new branch for the changes.  Choose a different
@@ -70,17 +73,17 @@ workflow may be helpful:
 
   * Create patch files 0001-*, 0002-*, ...
 
-      git format-patch master
+      git format-patch main
 
   * After reviewing the patch files, send the patches to tz@iana.org
     for others to review.
 
-      git send-email master
+      git send-email main
 
     For an archived example of such an email, see
     <https://mm.icann.org/pipermail/tz/2018-February/026122.html>.
 
-  * Start anew by getting current with the master branch again
+  * Start anew by getting current with the main branch again
     (the second step above).
 
 Please do not create issues or pull requests on GitHub, as the
diff --git a/Makefile b/Makefile
index 1136af9298f1..33f31684114b 100644
--- a/Makefile
+++ b/Makefile
@@ -45,9 +45,9 @@ LOCALTIME=	GMT
 #
 # Any other value for POSIXRULES is obsolete and should not be relied on, as:
 # * It does not work correctly in popular implementations such as GNU/Linux.
-# * It does not work in the tzdb implementation for timestamps after 2037.
-# * It is incompatible with 'zic -b slim' if POSIXRULES specifies transitions
-#   at standard time or UT rather than at local time.
+# * It does not work even in tzcode, except for historical timestamps
+#   that precede the last explicit transition in the POSIXRULES file.
+#   Hence it typically does not work for current and future timestamps.
 # In short, software should avoid ruleless settings like TZ='EET-2EEST'
 # and so should not depend on the value of POSIXRULES.
 #
@@ -122,8 +122,8 @@ LIBDIR = $(TOPDIR)/$(USRDIR)/lib
 
 # Types to try, as an alternative to time_t.
 TIME_T_ALTERNATIVES = $(TIME_T_ALTERNATIVES_HEAD) $(TIME_T_ALTERNATIVES_TAIL)
-TIME_T_ALTERNATIVES_HEAD = int64_t
-TIME_T_ALTERNATIVES_TAIL = int32_t uint32_t uint64_t
+TIME_T_ALTERNATIVES_HEAD = int_least64_t
+TIME_T_ALTERNATIVES_TAIL = int_least32_t uint_least32_t uint_least64_t
 
 # What kind of TZif data files to generate.  (TZif is the binary time
 # zone data format that zic generates; see Internet RFC 8536.)
@@ -152,8 +152,10 @@ REDO=		posix_right
 # The EXPIRES_LINE value matters only if REDO's value contains "right".
 # If you change EXPIRES_LINE, remove the leapseconds file before running "make".
 # zic's support for the Expires line was introduced in tzdb 2020a,
-# and EXPIRES_LINE defaults to 0 for now so that the leapseconds file
-# can be given to older zic implementations.
+# and was modified in tzdb 2021b to generate version 4 TZif files.
+# EXPIRES_LINE defaults to 0 for now so that the leapseconds file
+# can be given to pre-2020a zic implementations and so that TZif files
+# built by newer zic implementations can be read by pre-2021b libraries.
 EXPIRES_LINE=	0
 
 # To install data in text form that has all the information of the TZif data,
@@ -210,6 +212,7 @@ LDLIBS=
 #  -DHAVE_LOCALTIME_R=0 if your system lacks a localtime_r function
 #  -DHAVE_LOCALTIME_RZ=0 if you do not want zdump to use localtime_rz
 #	localtime_rz can make zdump significantly faster, but is nonstandard.
+#  -DHAVE_MALLOC_ERRNO=0 if malloc etc. do not set errno on failure.
 #  -DHAVE_POSIX_DECLS=0 if your system's include files do not declare
 #	functions like 'link' or variables like 'tzname' required by POSIX
 #  -DHAVE_SNPRINTF=0 if your system lacks the snprintf function
@@ -220,7 +223,6 @@ LDLIBS=
 #  -DHAVE_STRTOLL=0 if your system lacks the strtoll function
 #  -DHAVE_SYMLINK=0 if your system lacks the symlink function
 #  -DHAVE_SYS_STAT_H=0 if your compiler lacks a <sys/stat.h>
-#  -DHAVE_SYS_WAIT_H=0 if your compiler lacks a <sys/wait.h>
 #  -DHAVE_TZSET=0 if your system lacks a tzset function
 #  -DHAVE_UNISTD_H=0 if your compiler lacks a <unistd.h>
 #  -Dlocale_t=XXX if your system uses XXX instead of locale_t
@@ -257,22 +259,26 @@ LDLIBS=
 GCC_INSTRUMENT = \
   -fsanitize=undefined -fsanitize-address-use-after-scope \
   -fsanitize-undefined-trap-on-error -fstack-protector
+# Omit -fanalyzer from GCC_DEBUG_FLAGS, as it makes GCC too slow.
 GCC_DEBUG_FLAGS = -DGCC_LINT -g3 -O3 -fno-common \
   $(GCC_INSTRUMENT) \
   -Wall -Wextra \
   -Walloc-size-larger-than=100000 -Warray-bounds=2 \
   -Wbad-function-cast -Wcast-align=strict -Wdate-time \
   -Wdeclaration-after-statement -Wdouble-promotion \
+  -Wduplicated-branches -Wduplicated-cond \
   -Wformat=2 -Wformat-overflow=2 -Wformat-signedness -Wformat-truncation \
-  -Winit-self -Wjump-misses-init -Wlogical-op \
+  -Winit-self -Wlogical-op \
   -Wmissing-declarations -Wmissing-prototypes -Wnested-externs \
+  -Wnull-dereference \
   -Wold-style-definition -Woverlength-strings -Wpointer-arith \
-  -Wshadow -Wshift-overflow=2 -Wstrict-prototypes -Wstringop-overflow=4 \
+  -Wshadow -Wshift-overflow=2 -Wstrict-overflow \
+  -Wstrict-prototypes -Wstringop-overflow=4 \
   -Wstringop-truncation -Wsuggest-attribute=cold \
   -Wsuggest-attribute=const -Wsuggest-attribute=format \
   -Wsuggest-attribute=malloc \
   -Wsuggest-attribute=noreturn -Wsuggest-attribute=pure \
-  -Wtrampolines -Wundef -Wuninitialized -Wunused \
+  -Wtrampolines -Wundef -Wuninitialized -Wunused-macros \
   -Wvariadic-macros -Wvla -Wwrite-strings \
   -Wno-address -Wno-format-nonliteral -Wno-sign-compare \
   -Wno-type-limits -Wno-unused-parameter
@@ -523,7 +529,7 @@ TZS_YEAR=	2050
 TZS_CUTOFF_FLAG=	-c $(TZS_YEAR)
 TZS=		to$(TZS_YEAR).tzs
 TZS_NEW=	to$(TZS_YEAR)new.tzs
-TZS_DEPS=	$(PRIMARY_YDATA) asctime.c localtime.c \
+TZS_DEPS=	$(YDATA) asctime.c localtime.c \
 			private.h tzfile.h zdump.c zic.c
 # EIGHT_YARDS is just a yard short of the whole ENCHILADA.
 EIGHT_YARDS = $(COMMON) $(DOCS) $(SOURCES) $(DATA) $(MISC) tzdata.zi
@@ -796,9 +802,10 @@ check_links:	checklinks.awk $(TDATA_TO_CHECK) tzdata.zi
 		$(AWK) -f checklinks.awk tzdata.zi
 		touch $@
 
-check_tables:	checktab.awk $(PRIMARY_YDATA) $(ZONETABLES)
+check_tables:	checktab.awk $(YDATA) backward $(ZONETABLES)
 		for tab in $(ZONETABLES); do \
-		  $(AWK) -f checktab.awk -v zone_table=$$tab $(PRIMARY_YDATA) \
+		  test "$$tab" = zone.tab && links='$(BACKWARD)' || links=''; \
+		  $(AWK) -f checktab.awk -v zone_table=$$tab $(YDATA) $$links \
 		    || exit; \
 		done
 		touch $@
@@ -952,6 +959,12 @@ check_public: $(VERSION_DEPS)
 		  public.dir/zic -v -d public.dir/zoneinfo $$i 2>&1 || exit; \
 		done
 		public.dir/zic -v -d public.dir/zoneinfo-all $(TDATA_TO_CHECK)
+		:
+		: Also check 'backzone' syntax.
+		rm public.dir/main.zi
+		cd public.dir && $(MAKE) PACKRATDATA=backzone main.zi
+		public.dir/zic -d public.dir/zoneinfo main.zi
+		:
 		rm -fr public.dir
 		touch $@
 
@@ -964,7 +977,7 @@ $(TIME_T_ALTERNATIVES): $(VERSION_DEPS)
 		mkdir $@.dir
 		ln $(VERSION_DEPS) $@.dir
 		case $@ in \
-		  int32_t) range=-2147483648,2147483648;; \
+		  int*32_t) range=-2147483648,2147483648;; \
 		  u*) range=0,4294967296;; \
 		  *) range=-4294967296,4294967296;; \
 		esac && \
diff --git a/NEWS b/NEWS
index a60847beae81..d1ccf4e0fb7b 100644
--- a/NEWS
+++ b/NEWS
@@ -1,5 +1,228 @@
 News for the tz database
 
+Release 2021b - 2021-09-24 16:23:00 -0700
+
+  Briefly:
+    Jordan now starts DST on February's last Thursday.
+    Samoa no longer observes DST.
+    Merge more location-based Zones whose timestamps agree since 1970.
+    Move some backward-compatibility links to 'backward'.
+    Rename Pacific/Enderbury to Pacific/Kanton.
+    Correct many pre-1993 transitions in Malawi, Portugal, etc.
+    zic now creates each output file or link atomically.
+    zic -L no longer omits the POSIX TZ string in its output.
+    zic fixes for truncation and leap second table expiration.
+    zic now follows POSIX for TZ strings using all-year DST.
+    Fix some localtime crashes and bugs in obscure cases.
+    zdump -v now outputs more-useful boundary cases.
+    tzfile.5 better matches a draft successor to RFC 8536.
+    A new file SECURITY.
+
+  This release is prompted by recent announcements by Jordan and Samoa.
+  It incorporates many other changes that had accumulated since 2021a.
+  However, it omits most proposed changes that merged all Zones
+  agreeing since 1970, as concerns were raised about doing too many of
+  these changes at once.  It does keeps some of these changes in the
+  interest of making tzdb more equitable one step at a time; see
+  "Merge more location-based Zones" below.
+
+  Changes to future timestamps
+
+    Jordan now starts DST on February's last Thursday.
+    (Thanks to Steffen Thorsen.)
+
+    Samoa no longer observes DST.  (Thanks to Geoffrey D. Bennett.)
+
+  Changes to zone name
+
+    Rename Pacific/Enderbury to Pacific/Kanton.  When we added
+    Enderbury in 1993, we did not know that it is uninhabited and that
+    Kanton (population two dozen) is the only inhabited location in
+    that timezone.  The old name is now a backward-compatility link.
+
+  Changes to past timestamps
+
+    Correct many pre-1993 transitions, fixing entries originally
+    derived from Shanks, Whitman, and Mundell.  The fixes include:
+      - Barbados: standard time was introduced in 1911, not 1932; and
+	DST was observed in 1942-1944
+      - Cook Islands: In 1899 they switched from east to west of GMT,
+	celebrating Christmas for two days.  They (and Niue) switched
+	to standard time in 1952, not 1901.
+      - Guyana: corrected LMT for Georgetown; the introduction of
+	standard time in 1911, not 1915; and corrections to 1975 and
+	1992 transitions
+      - Kanton: uninhabited before 1937-08-31
+      - Niue: only observed -11:20 from 1952 through 1964, then went to
+        -11 instead of -11:30
+      - Portugal: DST was observed in 1950
+      - Tonga: corrected LMT; the introduction of standard time in 1945,
+        not 1901; and corrections to the transition from +12:20 to +13
+        in 1961, not 1941
+    Additional fixes to entries in the 'backzone' file include:
+      - Enderbury: inhabited only 1860/1885 and 1938-03-06/1942-02-09
+      - The Gambia: 1933 and 1942 transitions
+      - Malawi: several 1911 through 1925 transitions
+      - Sierra Leone: several 1913 through 1941 transitions, and DST
+	was NOT observed in 1957 through 1962
+    (Thanks to P Chan, Michael Deckers, Alexander Krivenyshev and
+    Alois Treindl.)
+
+    Merge more location-based Zones whose timestamps agree since 1970,
+    as pre-1970 timestamps are out of scope.  This is part of a
+    process that has been ongoing since 2013.  This does not affect
+    post-1970 timestamps, and timezone historians who build with 'make
+    PACKRATDATA=backzone' should see no changes to pre-1970 timestamps.
+    When merging, keep the most-populous location's data, and move
+    data for other locations to 'backzone' with a backward
+    link in 'backward'.  For example, move America/Creston data to
+    'backzone' with a link in 'backward' from America/Phoenix because
+    the two timezones' timestamps agree since 1970; this change
+    affects some pre-1968 timestamps in America/Creston because
+    Creston and Phoenix disagreed before 1968.  The affected Zones
+    are Africa/Accra, America/Atikokan, America/Blanc-Sablon,
+    America/Creston, America/Curacao, America/Nassau,
+    America/Port_of_Spain, Antarctica/DumontDUrville, and
+    Antarctica/Syowa.
+
+  Changes to maintenance procedure
+
+    The new file SECURITY covers how to report security-related bugs.
+
+    Several backward-compatibility links have been moved to the
+    'backward' file.  These links, which range from Africa/Addis_Ababa
+    to Pacific/Saipan, are only for compatibility with now-obsolete
+    guidelines suggesting an entry for every ISO 3166 code.
+    The intercontinental convenience links Asia/Istanbul and
+    Europe/Nicosia have also been moved to 'backward'.
+
+  Changes to code
+
+    zic now creates each output file or link atomically,
+    possibly by creating a temporary file and then renaming it.
+    This avoids races where a TZ setting would temporarily stop
+    working while zic was installing a replacement file or link.
+
+    zic -L no longer omits the POSIX TZ string in its output.
+    Starting with 2020a, zic -L truncated its output according to the
+    "Expires" directive or "#expires" comment in the leapseconds file.
+    The resulting TZif files omitted daylight saving transitions after
+    the leap second table expired, which led to far less-accurate
+    predictions of times after the expiry.  Although future timestamps
+    cannot be converted accurately in the presence of leap seconds, it
+    is more accurate to convert near-future timestamps with a few
+    seconds error than with an hour error, so zic -L no longer
+    truncates output in this way.
+
+    Instead, when zic -L is given the "Expires" directive, it now
+    outputs the expiration by appending a no-change entry to the leap
+    second table.  Although this should work well with most TZif
+    readers, it does not conform to Internet RFC 8536 and some pickier
+    clients (including tzdb 2017c through 2021a) reject it, so
+    "Expires" directives are currently disabled by default.  To enable
+    them, set the EXPIRES_LINE Makefile variable.  If a TZif file uses
+    this new feature it is marked with a new TZif version number 4,
+    a format intended to be documented in a successor to RFC 8536.
+
+    zic -L LEAPFILE -r @LO no longer generates an invalid TZif file
+    that omits leap second information for the range LO..B when LO
+    falls between two leap seconds A and B.  Instead, it generates a
+    TZif version 4 file that represents the previously-missing
+    information.
+
+    The TZif reader now allows the leap second table to begin with a
+    correction other than -1 or +1, and to contain adjacent
+    transitions with equal corrections.  This supports TZif version 4.
+
+    The TZif reader now lets leap seconds occur less than 28 days
+    apart.  This supports possible future TZif extensions.
+
+    Fix bug that caused 'localtime' etc. to crash when TZ was
+    set to a all-year DST string like "EST5EDT4,0/0,J365/25" that does
+    not conform to POSIX but does conform to Internet RFC 8536.
+
+    Fix another bug that caused 'localtime' etc. to crash when TZ was
+    set to a POSIX-conforming but unusual TZ string like
+    "EST5EDT4,0/0,J365/0", where almost all the year is DST.
+
+    Fix yet another bug that caused 'localtime' etc. to mishandle slim
+    TZif files containing leap seconds after the last explicit
+    transition in the table, or when handling far-future timestamps
+    in slim TZif files lacking leap seconds.
+
+    Fix localtime misbehavior involving positive leap seconds.
+    This change affects only behavior for "right" system time,
+    which contains leap seconds, and only if the UT offset is
+    not a multiple of 60 seconds when a positive leap second occurs.
+    (No such timezone exists in tzdb, luckily.)  Without the fix,
+    the timestamp was ambiguous during a positive leap second.
+    With the fix, any seconds occurring after a positive leap second
+    and within the same localtime minute are counted through 60, not
+    through 59; their UT offset (tm_gmtoff) is the same as before.
+    Here is how the fix affects timestamps in a timezone with UT
+    offset +01:23:45 (5025 seconds) and with a positive leap second at
+    1972-06-30 23:59:60 UTC (78796800):
+
+	time_t    without the fix      with the fix
+	78796800  1972-07-01 01:23:45  1972-07-01 01:23:45 (leap second)
+	78796801  1972-07-01 01:23:45  1972-07-01 01:23:46
+	...
+	78796815  1972-07-01 01:23:59  1972-07-01 01:23:60
+	78796816  1972-07-01 01:24:00  1972-07-01 01:24:00
+
+    Fix an unlikely bug that caused 'localtime' etc. to misbehave if
+    civil time changes a few seconds before time_t wraps around, when
+    leap seconds are enabled.
+
+    Fix bug in zic -r; in some cases, the dummy time type after the
+    last time transition disagreed with the TZ string, contrary to
+    Internet RFC 8563 section 3.3.
+
+    Fix a bug with 'zic -r @X' when X is a negative leap second that
+    has a nonnegative correction.  Without the fix, the output file
+    was truncated so that X appeared to be a positive leap second.
+    Fix a similar, even-less-likely bug when truncating at a positive
+    leap second that has a nonpositive correction.
+
+    zic -r now reports an error if given rolling leap seconds, as this
+    usage has never generally worked and is evidently unused.
+
+    zic now generates a POSIX-conforming TZ string for TZif files
+    where all-year DST is predicted for the indefinite future.
+    For example, for all-year Eastern Daylight Time, zic now generates
+    "XXX3EDT4,0/0,J365/23" where it previously generated
+    "EST5EDT,0/0,J365/25" or "".  (Thanks to Michael Deckers for
+    noting the possibility of POSIX conformance.)
+
+    zic.c no longer requires sys/wait.h (thanks to spazmodius for
+    noting it wasn't needed).
+
+    When reading slim TZif files, zdump no longer mishandles leap
+    seconds on the rare platforms where time_t counts leap seconds,
+    fixing a bug introduced in 2014g.
+
+    zdump -v now outputs timestamps at boundaries of what localtime
+    and gmtime can represent, instead of the less-useful timestamps
+    one day after the minimum and one day before the maximum.
+    (Thanks to Arthur David Olson for prototype code, and to Manuela
+    Friedrich for debugging help.)
+
+    zdump's -c and -t options are now consistently inclusive for the
+    lower time bound and exclusive for the upper.  Formerly they were
+    inconsistent.  (Confusion noted by Martin Burnicki.)
+
+  Changes to build procedure
+
+    You can now compile with -DHAVE_MALLOC_ERRNO=0 to port to
+    non-POSIX hosts where malloc doesn't set errno.
+    (Problem reported by Jan Engelhardt.)
+
+  Changes to documentation
+
+    tzfile.5 better matches a draft successor to RFC 8536
+    <https://datatracker.ietf.org/doc/draft-murchison-rfc8536bis/01/>.
+
+
 Release 2021a - 2021-01-24 10:54:57 -0800
 
   Changes to future timestamps
@@ -31,7 +254,7 @@ Release 2020e - 2020-12-22 15:14:34 -0800
     Correct many pre-1986 transitions, fixing entries originally
     derived from Shanks.  The fixes include:
       - Australia: several 1917 through 1971 transitions
-      - Bahamas: several 1941 through 1945 transitions
+      - The Bahamas: several 1941 through 1945 transitions
       - Bermuda: several 1917 through 1956 transitions
       - Belize: several 1942 through 1968 transitions
       - Ghana: several 1915 through 1956 transitions
@@ -825,8 +1048,8 @@ Release 2018d - 2018-03-22 07:05:46 -0700
     Institute in Montevideo.
     (Thanks to Jeremie Bonjour, Tim Parenti, and Michael Deckers.)
 
-    Enderbury and Kiritimati skipped New Year's Eve 1994, not
-    New Year's Day 1995.  (Thanks to Kerry Shetline.)
+    East Kiribati skipped New Year's Eve 1994, not New Year's Day 1995.
+    (Thanks to Kerry Shetline.)
 
     Fix the 1912-01-01 transition for Portugal and its colonies.
     This transition was at 00:00 according to the new UT offset, not
diff --git a/africa b/africa
index 28168cfc17f8..c73f0df3785c 100644
--- a/africa
+++ b/africa
@@ -30,9 +30,6 @@
 # Milne J. Civil time. Geogr J. 1899 Feb;13(2):173-94.
 # https://www.jstor.org/stable/1774359
 #
-# A reliable and entertaining source about time zones is
-# Derek Howse, Greenwich time and longitude, Philip Wilson Publishers (1997).
-#
 # European-style abbreviations are commonly used along the Mediterranean.
 # For sub-Saharan Africa abbreviations were less standardized.
 # Previous editions of this database used WAT, CAT, SAT, and EAT
@@ -153,15 +150,6 @@ Zone	Africa/Ndjamena	1:00:12 -	LMT	1912        # N'Djamena
 # Zone	NAME		STDOFF	RULES	FORMAT	[UNTIL]
 Zone	Africa/Abidjan	-0:16:08 -	LMT	1912
 			 0:00	-	GMT
-Link Africa/Abidjan Africa/Bamako	# Mali
-Link Africa/Abidjan Africa/Banjul	# Gambia
-Link Africa/Abidjan Africa/Conakry	# Guinea
-Link Africa/Abidjan Africa/Dakar	# Senegal
-Link Africa/Abidjan Africa/Freetown	# Sierra Leone
-Link Africa/Abidjan Africa/Lome		# Togo
-Link Africa/Abidjan Africa/Nouakchott	# Mauritania
-Link Africa/Abidjan Africa/Ouagadougou	# Burkina Faso
-Link Africa/Abidjan Atlantic/St_Helena	# St Helena
 
 # Djibouti
 # See Africa/Nairobi.
@@ -381,93 +369,8 @@ Zone	Africa/Cairo	2:05:09 -	LMT	1900 Oct
 # Gabon
 # See Africa/Lagos.
 
-# Gambia
-# See Africa/Abidjan.
-
+# The Gambia
 # Ghana
-
-# From P Chan (2020-11-20):
-# Interpretation Amendment Ordinance, 1915 (No.24 of 1915) [1915-11-02]
-# Ordinances of the Gold Coast, Ashanti, Northern Territories 1915, p 69-71
-# https://books.google.com/books?id=ErA-AQAAIAAJ&pg=PA70
-# This Ordinance added "'Time' shall mean Greenwich Mean Time" to the
-# Interpretation Ordinance, 1876.
-#
-# Determination of the Time Ordinance, 1919 (No. 18 of 1919) [1919-11-24]
-# Ordinances of the Gold Coast, Ashanti, Northern Territories 1919, p 75-76
-# https://books.google.com/books?id=MbA-AQAAIAAJ&pg=PA75
-# This Ordinance removed the previous definition of time and introduced DST.
-#
-# Time Determination Ordinance (Cap. 214)
-# The Laws of the Gold Coast (including Togoland Under British Mandate)
-# Vol. II (1937), p 2328
-# https://books.google.com/books?id=Z7M-AQAAIAAJ&pg=PA2328
-# Revised edition of the 1919 Ordinance.
-#
-# Time Determination (Amendment) Ordinance, 1940 (No. 9 of 1940) [1940-04-06]
-# Annual Volume of the Laws of the Gold Coast:
-# Containing All Legislation Enacted During Year 1940, p 22
-# https://books.google.com/books?id=1ao-AQAAIAAJ&pg=PA22
-# This Ordinance changed the forward transition from September to May.
-#
-# Defence (Time Determination Ordinance Amendment) Regulations, 1942
-# (Regulations No. 6 of 1942) [1942-01-31, commenced on 1942-02-08]
-# Annual Volume of the Laws of the Gold Coast:
-# Containing All Legislation Enacted During Year 1942, p 48
-# https://books.google.com/books?id=Das-AQAAIAAJ&pg=PA48
-# These regulations advanced the [standard] time by thirty minutes.
-#
-# Defence (Time Determination Ordinance Amendment (No.2)) Regulations,
-# 1942 (Regulations No. 28 of 1942) [1942-04-25]
-# Annual Volume of the Laws of the Gold Coast:
-# Containing All Legislation Enacted During Year 1942, p 87
-# https://books.google.com/books?id=Das-AQAAIAAJ&pg=PA87
-# These regulations abolished DST and changed the time to GMT+0:30.
-#
-# Defence (Revocation) (No.4) Regulations, 1945 (Regulations No. 45 of
-# 1945) [1945-10-24, commenced on 1946-01-06]
-# Annual Volume of the Laws of the Gold Coast:
-# Containing All Legislation Enacted During Year 1945, p 256
-# https://books.google.com/books?id=9as-AQAAIAAJ&pg=PA256
-# These regulations revoked the previous two sets of Regulations.
-#
-# Time Determination (Amendment) Ordinance, 1945 (No. 18 of 1945) [1946-01-06]
-# Annual Volume of the Laws of the Gold Coast:
-# Containing All Legislation Enacted During Year 1945, p 69
-# https://books.google.com/books?id=9as-AQAAIAAJ&pg=PA69
-# This Ordinance abolished DST.
-#
-# Time Determination (Amendment) Ordinance, 1950 (No. 26 of 1950) [1950-07-22]
-# Annual Volume of the Laws of the Gold Coast:
-# Containing All Legislation Enacted During Year 1950, p 35
-# https://books.google.com/books?id=e60-AQAAIAAJ&pg=PA35
-# This Ordinance restored DST but with thirty minutes offset.
-#
-# Time Determination Ordinance (Cap. 264)
-# The Laws of the Gold Coast, Vol. V (1954), p 380
-# https://books.google.com/books?id=Mqc-AQAAIAAJ&pg=PA380
-# Revised edition of the Time Determination Ordinance.
-#
-# Time Determination (Amendment) Ordinance, 1956 (No. 21 of 1956) [1956-08-29]
-# Annual Volume of the Ordinances of the Gold Coast Enacted During the
-# Year 1956, p 83
-# https://books.google.com/books?id=VLE-AQAAIAAJ&pg=PA83
-# This Ordinance abolished DST.
-
-# Rule	NAME	FROM	TO	-	IN	ON	AT	SAVE	LETTER/S
-Rule	Ghana	1919	only	-	Nov	24	0:00	0:20	+0020
-Rule	Ghana	1920	1942	-	Jan	 1	2:00	0	GMT
-Rule	Ghana	1920	1939	-	Sep	 1	2:00	0:20	+0020
-Rule	Ghana	1940	1941	-	May	 1	2:00	0:20	+0020
-Rule	Ghana	1950	1955	-	Sep	 1	2:00	0:30	+0030
-Rule	Ghana	1951	1956	-	Jan	 1	2:00	0	GMT
-
-# Zone	NAME		STDOFF	RULES	FORMAT	[UNTIL]
-Zone	Africa/Accra	-0:00:52 -	LMT	1915 Nov  2
-			 0:00	Ghana	%s	1942 Feb  8
-			 0:30	-	+0030	1946 Jan  6
-			 0:00	Ghana	%s
-
 # Guinea
 # See Africa/Abidjan.
 
@@ -533,15 +436,6 @@ Zone	Africa/Nairobi	2:27:16	-	LMT	1908 May
 			2:30	-	+0230	1936 Dec 31 24:00
 			2:45	-	+0245	1942 Jul 31 24:00
 			3:00	-	EAT
-Link Africa/Nairobi Africa/Addis_Ababa	 # Ethiopia
-Link Africa/Nairobi Africa/Asmara	 # Eritrea
-Link Africa/Nairobi Africa/Dar_es_Salaam # Tanzania
-Link Africa/Nairobi Africa/Djibouti
-Link Africa/Nairobi Africa/Kampala	 # Uganda
-Link Africa/Nairobi Africa/Mogadishu	 # Somalia
-Link Africa/Nairobi Indian/Antananarivo	 # Madagascar
-Link Africa/Nairobi Indian/Comoro
-Link Africa/Nairobi Indian/Mayotte
 
 # Lesotho
 # See Africa/Johannesburg.
@@ -732,7 +626,7 @@ Zone Indian/Mauritius	3:50:00 -	LMT	1907 # Port Louis
 # See Africa/Nairobi.
 
 # Morocco
-# See the 'europe' file for Spanish Morocco (Africa/Ceuta).
+# See Africa/Ceuta for Spanish Morocco.
 
 # From Alex Krivenyshev (2008-05-09):
 # Here is an article that Morocco plan to introduce Daylight Saving Time between
@@ -1228,13 +1122,6 @@ Zone Africa/El_Aaiun	-0:52:48 -	LMT	1934 Jan # El Aaiún
 # Zone	NAME		STDOFF	RULES	FORMAT	[UNTIL]
 Zone	Africa/Maputo	2:10:20 -	LMT	1903 Mar
 			2:00	-	CAT
-Link Africa/Maputo Africa/Blantyre	# Malawi
-Link Africa/Maputo Africa/Bujumbura	# Burundi
-Link Africa/Maputo Africa/Gaborone	# Botswana
-Link Africa/Maputo Africa/Harare	# Zimbabwe
-Link Africa/Maputo Africa/Kigali	# Rwanda
-Link Africa/Maputo Africa/Lubumbashi	# E Dem. Rep. of Congo
-Link Africa/Maputo Africa/Lusaka	# Zambia
 
 
 # Namibia
@@ -1382,23 +1269,12 @@ Zone	Africa/Lagos	0:13:35 -	LMT	1905 Jul  1
 			0:13:35	-	LMT	1914 Jan  1
 			0:30	-	+0030	1919 Sep  1
 			1:00	-	WAT
-Link Africa/Lagos Africa/Bangui	     # Central African Republic
-Link Africa/Lagos Africa/Brazzaville # Rep. of the Congo
-Link Africa/Lagos Africa/Douala	     # Cameroon
-Link Africa/Lagos Africa/Kinshasa    # Dem. Rep. of the Congo (west)
-Link Africa/Lagos Africa/Libreville  # Gabon
-Link Africa/Lagos Africa/Luanda	     # Angola
-Link Africa/Lagos Africa/Malabo	     # Equatorial Guinea
-Link Africa/Lagos Africa/Niamey	     # Niger
-Link Africa/Lagos Africa/Porto-Novo  # Benin
 
 # Réunion
 # Zone	NAME		STDOFF	RULES	FORMAT	[UNTIL]
 Zone	Indian/Reunion	3:41:52 -	LMT	1911 Jun # Saint-Denis
 			4:00	-	+04
 #
-# Crozet Islands also observes Réunion time; see the 'antarctica' file.
-#
 # Scattered Islands (Îles Éparses) administered from Réunion are as follows.
 # The following information about them is taken from
 # Îles Éparses (<http://www.outre-mer.gouv.fr/domtom/ile.htm>, 1997-07-22,
@@ -1490,8 +1366,6 @@ Rule	SA	1943	1944	-	Mar	Sun>=15	2:00	0	-
 Zone Africa/Johannesburg 1:52:00 -	LMT	1892 Feb 8
 			1:30	-	SAST	1903 Mar
 			2:00	SA	SAST
-Link Africa/Johannesburg Africa/Maseru	   # Lesotho
-Link Africa/Johannesburg Africa/Mbabane    # Eswatini
 #
 # Marion and Prince Edward Is
 # scientific station since 1947
@@ -1527,12 +1401,13 @@ Zone	Africa/Khartoum	2:10:08 -	LMT	1931
 			3:00	-	EAT	2017 Nov  1
 			2:00	-	CAT
 
+# South Sudan
+
 # From Steffen Thorsen (2021-01-18):
 # "South Sudan will change its time zone by setting the clock back 1
 # hour on February 1, 2021...."
 # from https://eyeradio.org/south-sudan-adopts-new-time-zone-makuei/
 
-# South Sudan
 # Zone	NAME		STDOFF	RULES	FORMAT	[UNTIL]
 Zone	Africa/Juba	2:06:28 -	LMT	1931
 			2:00	Sudan	CA%sT	2000 Jan 15 12:00
@@ -1637,7 +1512,7 @@ Rule	Tunisia	2005	only	-	Sep	30	 1:00s	0	-
 Rule	Tunisia	2006	2008	-	Mar	lastSun	 2:00s	1:00	S
 Rule	Tunisia	2006	2008	-	Oct	lastSun	 2:00s	0	-
 
-# See Europe/Paris for PMT-related transitions.
+# See Europe/Paris commentary for PMT-related transitions.
 # Zone	NAME		STDOFF	RULES	FORMAT	[UNTIL]
 Zone	Africa/Tunis	0:40:44 -	LMT	1881 May 12
 			0:09:21	-	PMT	1911 Mar 11 # Paris Mean Time
diff --git a/antarctica b/antarctica
index ed750a899217..70a5422a9e0a 100644
--- a/antarctica
+++ b/antarctica
@@ -148,7 +148,7 @@ Zone Antarctica/Mawson	0	-	-00	1954 Feb 13
 #
 # Alfred Faure, Possession Island, Crozet Islands, -462551+0515152, since 1964;
 #	sealing & whaling stations operated variously 1802/1911+;
-#	see Indian/Reunion.
+#	see Asia/Dubai.
 #
 # Martin-de-Viviès, Amsterdam Island, -374105+0773155, since 1950
 # Port-aux-Français, Kerguelen Islands, -492110+0701303, since 1951;
@@ -162,17 +162,7 @@ Zone Indian/Kerguelen	0	-	-00	1950 # Port-aux-Français
 			5:00	-	+05
 #
 # year-round base in the main continent
-# Dumont d'Urville, Île des Pétrels, -6640+14001, since 1956-11
-# <https://en.wikipedia.org/wiki/Dumont_d'Urville_Station> (2005-12-05)
-#
-# Another base at Port-Martin, 50km east, began operation in 1947.
-# It was destroyed by fire on 1952-01-14.
-#
-# Zone	NAME		STDOFF	RULES	FORMAT	[UNTIL]
-Zone Antarctica/DumontDUrville 0 -	-00	1947
-			10:00	-	+10	1952 Jan 14
-			0	-	-00	1956 Nov
-			10:00	-	+10
+# Dumont d'Urville - see Pacific/Port_Moresby.
 
 # France & Italy - year-round base
 # Concordia, -750600+1232000, since 2005
@@ -188,20 +178,7 @@ Zone Antarctica/DumontDUrville 0 -	-00	1947
 # Zuchelli, Terra Nova Bay, -744140+1640647, since 1986
 
 # Japan - year-round bases
-# Syowa (also known as Showa), -690022+0393524, since 1957
-#
-# From Hideyuki Suzuki (1999-02-06):
-# In all Japanese stations, +0300 is used as the standard time.
-#
-# Syowa station, which is the first antarctic station of Japan,
-# was established on 1957-01-29.  Since Syowa station is still the main
-# station of Japan, it's appropriate for the principal location.
-# Zone	NAME		STDOFF	RULES	FORMAT	[UNTIL]
-Zone Antarctica/Syowa	0	-	-00	1957 Jan 29
-			3:00	-	+03
-# See:
-# NIPR Antarctic Research Activities (1999-08-17)
-# http://www.nipr.ac.jp/english/ara01.html
+# See Asia/Riyadh.
 
 # S Korea - year-round base
 # Jang Bogo, Terra Nova Bay, -743700+1641205 since 2014
diff --git a/asia b/asia
index ed944130e99f..73e01831d09b 100644
--- a/asia
+++ b/asia
@@ -34,9 +34,6 @@
 # Byalokoz EL. New Counting of Time in Russia since July 1, 1919.
 # (See the 'europe' file for a fuller citation.)
 #
-# A reliable and entertaining source about time zones is
-# Derek Howse, Greenwich time and longitude, Philip Wilson Publishers (1997).
-#
 # The following alphabetic abbreviations appear in these tables
 # (corrections are welcome):
 #	     std  dst
@@ -1176,10 +1173,9 @@ Zone	Asia/Famagusta	2:15:48	-	LMT	1921 Nov 14
 			2:00	EUAsia	EE%sT	2016 Sep  8
 			3:00	-	+03	2017 Oct 29 1:00u
 			2:00	EUAsia	EE%sT
-
 # Classically, Cyprus belongs to Asia; e.g. see Herodotus, Histories, I.72.
 # However, for various reasons many users expect to find it under Europe.
-Link	Asia/Nicosia	Europe/Nicosia
+# See the 'backward' file for the Europe/Nicosia link.
 
 # Georgia
 # From Paul Eggert (1994-11-19):
@@ -2234,6 +2230,14 @@ Zone	Asia/Tokyo	9:18:59	-	LMT	1887 Dec 31 15:00u
 # From Paul Eggert (2013-12-11):
 # As Steffen suggested, consider the past 21-month experiment to be DST.
 
+# From Steffen Thorsen (2021-09-24):
+# The Jordanian Government announced yesterday that they will start DST
+# in February instead of March:
+# https://petra.gov.jo/Include/InnerPage.jsp?ID=37683&lang=en&name=en_news (English)
+# https://petra.gov.jo/Include/InnerPage.jsp?ID=189969&lang=ar&name=news (Arabic)
+# From the Arabic version, it seems to say it would be at midnight
+# (assume 24:00) on the last Thursday in February, starting from 2022.
+
 # Rule	NAME	FROM	TO	-	IN	ON	AT	SAVE	LETTER/S
 Rule	Jordan	1973	only	-	Jun	6	0:00	1:00	S
 Rule	Jordan	1973	1975	-	Oct	1	0:00	0	-
@@ -2264,8 +2268,9 @@ Rule	Jordan	2004	only	-	Oct	15	0:00s	0	-
 Rule	Jordan	2005	only	-	Sep	lastFri	0:00s	0	-
 Rule	Jordan	2006	2011	-	Oct	lastFri	0:00s	0	-
 Rule	Jordan	2013	only	-	Dec	20	0:00	0	-
-Rule	Jordan	2014	max	-	Mar	lastThu	24:00	1:00	S
+Rule	Jordan	2014	2021	-	Mar	lastThu	24:00	1:00	S
 Rule	Jordan	2014	max	-	Oct	lastFri	0:00s	0	-
+Rule	Jordan	2022	max	-	Feb	lastThu	24:00	1:00	S
 # Zone	NAME		STDOFF	RULES	FORMAT	[UNTIL]
 Zone	Asia/Amman	2:23:44 -	LMT	1931
 			2:00	Jordan	EE%sT
@@ -2740,7 +2745,8 @@ Rule	NBorneo	1935	1941	-	Dec	14	0:00	0	-
 #
 # peninsular Malaysia
 # taken from Mok Ly Yng (2003-10-30)
-# http://www.math.nus.edu.sg/aslaksen/teaching/timezone.html
+# https://web.archive.org/web/20190822231045/http://www.math.nus.edu.sg/~mathelmr/teaching/timezone.html
+# This agrees with Singapore since 1905-06-01.
 # Zone	NAME		STDOFF	RULES	FORMAT	[UNTIL]
 Zone Asia/Kuala_Lumpur	6:46:46 -	LMT	1901 Jan  1
 			6:55:25	-	SMT	1905 Jun  1 # Singapore M.T.
@@ -3500,6 +3506,12 @@ Zone	Asia/Hebron	2:20:23	-	LMT	1900 Oct
 # influence of the sources.  There is no current abbreviation for DST,
 # so use "PDT", the usual American style.
 
+# From P Chan (2021-05-10):
+# Here's a fairly comprehensive article in Japanese:
+# https://wiki.suikawiki.org/n/Philippine%20Time
+# From Paul Eggert (2021-05-10):
+# The info in the Japanese table has not been absorbed (yet) below.
+
 # Rule	NAME	FROM	TO	-	IN	ON	AT	SAVE	LETTER/S
 Rule	Phil	1936	only	-	Nov	1	0:00	1:00	D
 Rule	Phil	1937	only	-	Feb	1	0:00	0	S
@@ -3519,7 +3531,6 @@ Zone	Asia/Manila	-15:56:00 -	LMT	1844 Dec 31
 Zone	Asia/Qatar	3:26:08 -	LMT	1920     # Al Dawhah / Doha
 			4:00	-	+04	1972 Jun
 			3:00	-	+03
-Link Asia/Qatar Asia/Bahrain
 
 # Saudi Arabia
 #
@@ -3566,12 +3577,10 @@ Link Asia/Qatar Asia/Bahrain
 # Zone	NAME		STDOFF	RULES	FORMAT	[UNTIL]
 Zone	Asia/Riyadh	3:06:52 -	LMT	1947 Mar 14
 			3:00	-	+03
-Link Asia/Riyadh Asia/Aden	# Yemen
-Link Asia/Riyadh Asia/Kuwait
 
 # Singapore
 # taken from Mok Ly Yng (2003-10-30)
-# http://www.math.nus.edu.sg/aslaksen/teaching/timezone.html
+# https://web.archive.org/web/20190822231045/http://www.math.nus.edu.sg/~mathelmr/teaching/timezone.html
 # Zone	NAME		STDOFF	RULES	FORMAT	[UNTIL]
 Zone	Asia/Singapore	6:55:25 -	LMT	1901 Jan  1
 			6:55:25	-	SMT	1905 Jun  1 # Singapore M.T.
@@ -3824,8 +3833,6 @@ Zone	Asia/Dushanbe	4:35:12 -	LMT	1924 May  2
 Zone	Asia/Bangkok	6:42:04	-	LMT	1880
 			6:42:04	-	BMT	1920 Apr # Bangkok Mean Time
 			7:00	-	+07
-Link Asia/Bangkok Asia/Phnom_Penh	# Cambodia
-Link Asia/Bangkok Asia/Vientiane	# Laos
 
 # Turkmenistan
 # From Shanks & Pottenger.
@@ -3840,7 +3847,6 @@ Zone	Asia/Ashgabat	3:53:32 -	LMT	1924 May  2 # or Ashkhabad
 # Zone	NAME		STDOFF	RULES	FORMAT	[UNTIL]
 Zone	Asia/Dubai	3:41:12 -	LMT	1920
 			4:00	-	+04
-Link Asia/Dubai Asia/Muscat	# Oman
 
 # Uzbekistan
 # Byalokoz 1919 says Uzbekistan was 4:27:53.
diff --git a/australasia b/australasia
index cf8a0638f831..8e76c270abc5 100644
--- a/australasia
+++ b/australasia
@@ -458,13 +458,12 @@ Zone	Pacific/Guam	-14:21:00 -	LMT	1844 Dec 31
 			 9:00	-	+09	1944 Jul 31
 			10:00	Guam	G%sT	2000 Dec 23
 			10:00	-	ChST	# Chamorro Standard Time
-Link Pacific/Guam Pacific/Saipan # N Mariana Is
 
 # Kiribati
 # Zone	NAME		STDOFF	RULES	FORMAT	[UNTIL]
 Zone Pacific/Tarawa	 11:32:04 -	LMT	1901 # Bairiki
 			 12:00	-	+12
-Zone Pacific/Enderbury	-11:24:20 -	LMT	1901
+Zone Pacific/Kanton	  0	-	-00	1937 Aug 31
 			-12:00	-	-12	1979 Oct
 			-11:00	-	-11	1994 Dec 31
 			 13:00	-	+13
@@ -584,8 +583,6 @@ Zone Pacific/Chatham	12:13:48 -	LMT	1868 Nov  2
 			12:15	-	+1215	1946 Jan  1
 			12:45	Chatham	+1245/+1345
 
-Link Pacific/Auckland Antarctica/McMurdo
-
 # Auckland Is
 # uninhabited; Māori and Moriori, colonial settlers, pastoralists, sealers,
 # and scientific personnel have wintered
@@ -597,13 +594,46 @@ Link Pacific/Auckland Antarctica/McMurdo
 # was probably like Pacific/Auckland
 
 # Cook Is
-# From Shanks & Pottenger:
+#
+# From Alexander Krivenyshev (2021-03-24):
+# In 1899 the Cook Islands celebrated Christmas twice to correct the calendar.
+# According to the old books, missionaries were unaware of
+# the International Date line, when they came from Sydney.
+# Thus the Cook Islands were one day ahead....
+# http://nzetc.victoria.ac.nz/tm/scholarly/tei-KloDisc-t1-body-d18.html
+# ... Appendix to the Journals of the House of Representatives, 1900
+# https://atojs.natlib.govt.nz/cgi-bin/atojs?a=d&d=AJHR1900-I.2.1.2.3
+# (page 20)
+#
+# From Michael Deckers (2021-03-24):
+# ... in the Cook Island Act of 1915-10-11, online at
+# http://www.paclii.org/ck/legis/ck-nz_act/cia1915132/
+# "651. The hour of the day shall in each of the islands included in the
+#  Cook Islands be determined in accordance with the meridian of that island."
+# so that local (mean?) time was still used in Rarotonga (and Niue) in 1915.
+# This was changed in the Cook Island Amendment Act of 1952-10-16 ...
+# http://www.paclii.org/ck/legis/ck-nz_act/ciaa1952212/
+# "651 (1) The hour of the day in each of the islands included in the Cook
+#  Islands, other than Niue, shall be determined as if each island were
+#  situated on the meridian one hundred and fifty-seven degrees thirty minutes
+#  West of Greenwich.  (2) The hour of the day in the Island of Niue shall be
+#  determined as if that island were situated on the meridian one hundred and
+#  seventy degrees West of Greenwich."
+# This act does not state when it takes effect, so one has to assume it
+# applies since 1952-10-16.  But there is the possibility that the act just
+# legalized prior existing practice, as we had seen with the Guernsey law of
+# 1913-06-18 for the switch in 1909-04-19.
+#
+# From Paul Eggert (2021-03-24):
+# Transitions after 1952 are from Shanks & Pottenger.
+#
 # Rule	NAME	FROM	TO	-	IN	ON	AT	SAVE	LETTER/S
 Rule	Cook	1978	only	-	Nov	12	0:00	0:30	-
 Rule	Cook	1979	1991	-	Mar	Sun>=1	0:00	0	-
 Rule	Cook	1979	1990	-	Oct	lastSun	0:00	0:30	-
 # Zone	NAME		STDOFF	RULES	FORMAT	[UNTIL]
-Zone Pacific/Rarotonga	-10:39:04 -	LMT	1901        # Avarua
+Zone Pacific/Rarotonga	13:20:56 -	LMT	1899 Dec 26 # Avarua
+			-10:39:04 -	LMT	1952 Oct 16
 			-10:30	-	-1030	1978 Nov 12
 			-10:00	Cook	-10/-0930
 
@@ -611,10 +641,18 @@ Zone Pacific/Rarotonga	-10:39:04 -	LMT	1901        # Avarua
 
 
 # Niue
+# See Pacific/Raratonga comments for 1952 transition.
+#
+# From Tim Parenti (2021-09-13):
+# Consecutive contemporaneous editions of The Air Almanac listed -11:20 for
+# Niue as of Apr 1964 but -11 as of Aug 1964:
+#   Apr 1964: https://books.google.com/books?id=_1So677Y5vUC&pg=SL1-PA23
+#   Aug 1964: https://books.google.com/books?id=MbJloqd-zyUC&pg=SL1-PA23
+# Without greater specificity, guess 1964-07-01 for this transition.
+
 # Zone	NAME		STDOFF	RULES	FORMAT	[UNTIL]
-Zone	Pacific/Niue	-11:19:40 -	LMT	1901        # Alofi
-			-11:20	-	-1120	1951
-			-11:30	-	-1130	1978 Oct  1
+Zone	Pacific/Niue	-11:19:40 -	LMT	1952 Oct 16	# Alofi
+			-11:20	-	-1120	1964 Jul
 			-11:00	-	-11
 
 # Norfolk
@@ -673,7 +711,6 @@ Zone Pacific/Pitcairn	-8:40:20 -	LMT	1901        # Adamstown
 Zone Pacific/Pago_Pago	 12:37:12 -	LMT	1892 Jul  5
 			-11:22:48 -	LMT	1911
 			-11:00	-	SST	            # S=Samoa
-Link Pacific/Pago_Pago Pacific/Midway # in US minor outlying islands
 
 # Samoa (formerly and also known as Western Samoa)
 
@@ -742,13 +779,17 @@ Link Pacific/Pago_Pago Pacific/Midway # in US minor outlying islands
 # From Paul Eggert (2014-07-08):
 # That web page currently lists transitions for 2012/3 and 2013/4.
 # Assume the pattern instituted in 2012 will continue indefinitely.
+#
+# From Geoffrey D. Bennett (2021-09-20):
+# https://www.mcil.gov.ws/storage/2021/09/MCIL-Scan_20210920_120553.pdf
+# DST has been cancelled for this year.
 
 # Rule	NAME	FROM	TO	-	IN	ON	AT	SAVE	LETTER/S
 Rule	WS	2010	only	-	Sep	lastSun	0:00	1	-
 Rule	WS	2011	only	-	Apr	Sat>=1	4:00	0	-
 Rule	WS	2011	only	-	Sep	lastSat	3:00	1	-
-Rule	WS	2012	max	-	Apr	Sun>=1	4:00	0	-
-Rule	WS	2012	max	-	Sep	lastSun	3:00	1	-
+Rule	WS	2012	2021	-	Apr	Sun>=1	4:00	0	-
+Rule	WS	2012	2020	-	Sep	lastSun	3:00	1	-
 # Zone	NAME		STDOFF	RULES	FORMAT	[UNTIL]
 Zone Pacific/Apia	 12:33:04 -	LMT	1892 Jul  5
 			-11:26:56 -	LMT	1911
@@ -795,8 +836,8 @@ Rule	Tonga	2001	2002	-	Jan	lastSun	2:00	0	-
 Rule	Tonga	2016	only	-	Nov	Sun>=1	2:00	1:00	-
 Rule	Tonga	2017	only	-	Jan	Sun>=15	3:00	0	-
 # Zone	NAME		STDOFF	RULES	FORMAT	[UNTIL]
-Zone Pacific/Tongatapu	12:19:20 -	LMT	1901
-			12:20	-	+1220	1941
+Zone Pacific/Tongatapu	12:19:12 -	LMT	1945 Sep 10
+			12:20	-	+1220	1961
 			13:00	-	+13	1999
 			13:00	Tonga	+13/+14
 
@@ -1738,6 +1779,23 @@ Zone	Pacific/Wallis	12:15:20 -	LMT	1901
 # One source for this is page 202 of: Bartky IR. One Time Fits All:
 # The Campaigns for Global Uniformity (2007).
 
+# Kanton
+
+# From Paul Eggert (2021-05-27):
+# Kiribati's +13 timezone is represented by Kanton, its only populated
+# island.  (It was formerly spelled "Canton", but Gilbertese lacks "C".)
+# Kanton was settled on 1937-08-31 by two British radio operators
+# <https://history.state.gov/historicaldocuments/frus1937v02/d94>;
+# Americans came the next year and built an airfield, partly to
+# establish airline service and perhaps partly anticipating the
+# next war.  Aside from the war, the airfield was used by commercial
+# airlines until long-range jets became standard; although currently
+# for emergency use only, China says it is considering rebuilding the
+# airfield for high-end niche tourism.  Kanton has about two dozen
+# people, caretakers who rotate in from the rest of Kiribati in 2-5
+# year shifts, and who use some of the leftover structures
+# <http://pipa.neaq.org/2012/06/images-of-kanton-island.html>.
+
 # Kwajalein
 
 # From an AP article (1993-08-22):
@@ -2021,6 +2079,17 @@ Zone	Pacific/Wallis	12:15:20 -	LMT	1901
 
 # Tonga
 
+# From Paul Eggert (2021-03-04):
+# In 1943 "The standard time kept is 12 hrs. 19 min. 12 sec. fast
+# on Greenwich mean time." according to the Admiralty's Hydrographic
+# Dept., Pacific Islands Pilot, Vol. II, 7th ed., 1943, p 360.
+
+# From Michael Deckers (2021-03-03):
+# [Ian R Bartky: "One Time Fits All: The Campaigns for Global Uniformity".
+# Stanford University Press. 2007. p. 255]:
+# On 10 September 1945 Tonga adopted a standard time 12 hours,
+# 20 minutes in advance of Greenwich.
+
 # From Paul Eggert (1996-01-22):
 # Today's _Wall Street Journal_ (p 1) reports that "Tonga has been plotting
 # to sneak ahead of [New Zealanders] by introducing daylight-saving time."
@@ -2049,9 +2118,26 @@ Zone	Pacific/Wallis	12:15:20 -	LMT	1901
 # The Crown Prince, presented an unanswerable argument: "Remember that
 # on the World Day of Prayer, you would be the first people on Earth
 # to say your prayers in the morning."
-
-# From Paul Eggert (2006-03-22):
-# Shanks & Pottenger say the transition was on 1968-10-01; go with Mundell.
+#
+# From Tim Parenti (2021-09-13), per Paul Eggert (2006-03-22) and Michael
+# Deckers (2021-03-03):
+# Mundell places the transition from +12:20 to +13 in 1941, while Shanks &
+# Pottenger say the transition was on 1968-10-01.
+#
+# The Air Almanac published contemporaneous tables of standard times,
+# which listed +12:20 as of Nov 1960 and +13 as of Mar 1961:
+#   Nov 1960: https://books.google.com/books?id=bVgtWM6kPZUC&pg=SL1-PA19
+#   Mar 1961: https://books.google.com/books?id=W2nItAul4g0C&pg=SL1-PA19
+# (Thanks to P Chan for pointing us toward these sources.)
+# This agrees with Bartky, who writes that "since 1961 [Tonga's] official time
+# has been thirteen hours in advance of Greenwich time" (p. 202) and further
+# writes in an endnote that this was because "the legislation was amended" on
+# 1960-10-19. (p. 255)
+#
+# Without greater specificity, presume that Bartky and the Air Almanac point to
+# a 1961-01-01 transition, as Tāufaʻāhau Tupou IV was still Crown Prince in
+# 1961 and this still jives with the gist of Mundell's telling, and go with
+# this over Shanks & Pottenger.
 
 # From Eric Ulevik (1999-05-03):
 # Tonga's director of tourism, who is also secretary of the National Millennium
diff --git a/backward b/backward
index 0c55be221df1..7c288e31b74e 100644
--- a/backward
+++ b/backward
@@ -3,50 +3,121 @@
 # This file is in the public domain, so clarified as of
 # 2009-05-17 by Arthur David Olson.
 
-# This file provides links between current names for timezones
-# and their old names.  Many names changed in late 1993.
+# This file provides links from old or merged timezone names to current ones.
+# Many names changed in late 1993, and many merged names moved here
+# in the period from 2013 through 2021.  Several of these names are
+# also present in the file 'backzone', which has data important only
+# for pre-1970 timestamps and so is out of scope for tzdb proper.
 
 # Link	TARGET			LINK-NAME
+Link	Africa/Abidjan		Africa/Accra
+Link	Africa/Nairobi		Africa/Addis_Ababa
+Link	Africa/Nairobi		Africa/Asmara
 Link	Africa/Nairobi		Africa/Asmera
+Link	Africa/Abidjan		Africa/Bamako
+Link	Africa/Lagos		Africa/Bangui
+Link	Africa/Abidjan		Africa/Banjul
+Link	Africa/Maputo		Africa/Blantyre
+Link	Africa/Lagos		Africa/Brazzaville
+Link	Africa/Maputo		Africa/Bujumbura
+Link	Africa/Abidjan		Africa/Conakry
+Link	Africa/Abidjan		Africa/Dakar
+Link	Africa/Nairobi		Africa/Dar_es_Salaam
+Link	Africa/Nairobi		Africa/Djibouti
+Link	Africa/Lagos		Africa/Douala
+Link	Africa/Abidjan		Africa/Freetown
+Link	Africa/Maputo		Africa/Gaborone
+Link	Africa/Maputo		Africa/Harare
+Link	Africa/Nairobi		Africa/Kampala
+Link	Africa/Maputo		Africa/Kigali
+Link	Africa/Lagos		Africa/Kinshasa
+Link	Africa/Lagos		Africa/Libreville
+Link	Africa/Abidjan		Africa/Lome
+Link	Africa/Lagos		Africa/Luanda
+Link	Africa/Maputo		Africa/Lubumbashi
+Link	Africa/Maputo		Africa/Lusaka
+Link	Africa/Lagos		Africa/Malabo
+Link	Africa/Johannesburg	Africa/Maseru
+Link	Africa/Johannesburg	Africa/Mbabane
+Link	Africa/Nairobi		Africa/Mogadishu
+Link	Africa/Lagos		Africa/Niamey
+Link	Africa/Abidjan		Africa/Nouakchott
+Link	Africa/Abidjan		Africa/Ouagadougou
+Link	Africa/Lagos		Africa/Porto-Novo
 Link	Africa/Abidjan		Africa/Timbuktu
+Link	America/Puerto_Rico	America/Anguilla
+Link	America/Puerto_Rico	America/Antigua
 Link	America/Argentina/Catamarca	America/Argentina/ComodRivadavia
+Link	America/Puerto_Rico	America/Aruba
+Link	America/Panama		America/Atikokan
 Link	America/Adak		America/Atka
+Link	America/Puerto_Rico	America/Blanc-Sablon
 Link	America/Argentina/Buenos_Aires	America/Buenos_Aires
 Link	America/Argentina/Catamarca	America/Catamarca
-Link	America/Atikokan	America/Coral_Harbour
+Link	America/Panama		America/Cayman
+Link	America/Panama		America/Coral_Harbour
 Link	America/Argentina/Cordoba	America/Cordoba
+Link	America/Phoenix		America/Creston
+Link	America/Puerto_Rico	America/Curacao
+Link	America/Puerto_Rico	America/Dominica
 Link	America/Tijuana		America/Ensenada
 Link	America/Indiana/Indianapolis	America/Fort_Wayne
 Link	America/Nuuk		America/Godthab
+Link	America/Puerto_Rico	America/Grenada
+Link	America/Puerto_Rico	America/Guadeloupe
 Link	America/Indiana/Indianapolis	America/Indianapolis
 Link	America/Argentina/Jujuy	America/Jujuy
 Link	America/Indiana/Knox	America/Knox_IN
+Link	America/Puerto_Rico	America/Kralendijk
 Link	America/Kentucky/Louisville	America/Louisville
+Link	America/Puerto_Rico	America/Lower_Princes
+Link	America/Puerto_Rico	America/Marigot
 Link	America/Argentina/Mendoza	America/Mendoza
 Link	America/Toronto		America/Montreal
+Link	America/Puerto_Rico	America/Montserrat
+Link	America/Toronto		America/Nassau
+Link	America/Puerto_Rico	America/Port_of_Spain
 Link	America/Rio_Branco	America/Porto_Acre
 Link	America/Argentina/Cordoba	America/Rosario
 Link	America/Tijuana		America/Santa_Isabel
 Link	America/Denver		America/Shiprock
-Link	America/Port_of_Spain	America/Virgin
+Link	America/Puerto_Rico	America/St_Barthelemy
+Link	America/Puerto_Rico	America/St_Kitts
+Link	America/Puerto_Rico	America/St_Lucia
+Link	America/Puerto_Rico	America/St_Thomas
+Link	America/Puerto_Rico	America/St_Vincent
+Link	America/Puerto_Rico	America/Tortola
+Link	America/Puerto_Rico	America/Virgin
+Link	Pacific/Port_Moresby	Antarctica/DumontDUrville
+Link	Pacific/Auckland	Antarctica/McMurdo
 Link	Pacific/Auckland	Antarctica/South_Pole
+Link	Asia/Riyadh		Antarctica/Syowa
+Link	Europe/Oslo		Arctic/Longyearbyen
+Link	Asia/Riyadh		Asia/Aden
 Link	Asia/Ashgabat		Asia/Ashkhabad
+Link	Asia/Qatar		Asia/Bahrain
 Link	Asia/Kolkata		Asia/Calcutta
 Link	Asia/Shanghai		Asia/Chongqing
 Link	Asia/Shanghai		Asia/Chungking
 Link	Asia/Dhaka		Asia/Dacca
 Link	Asia/Shanghai		Asia/Harbin
+Link	Europe/Istanbul		Asia/Istanbul
 Link	Asia/Urumqi		Asia/Kashgar
 Link	Asia/Kathmandu		Asia/Katmandu
+Link	Asia/Riyadh		Asia/Kuwait
 Link	Asia/Macau		Asia/Macao
+Link	Asia/Dubai		Asia/Muscat
+Link	Asia/Bangkok		Asia/Phnom_Penh
 Link	Asia/Yangon		Asia/Rangoon
 Link	Asia/Ho_Chi_Minh	Asia/Saigon
 Link	Asia/Jerusalem		Asia/Tel_Aviv
 Link	Asia/Thimphu		Asia/Thimbu
 Link	Asia/Makassar		Asia/Ujung_Pandang
 Link	Asia/Ulaanbaatar	Asia/Ulan_Bator
+Link	Asia/Bangkok		Asia/Vientiane
 Link	Atlantic/Faroe		Atlantic/Faeroe
-Link	Europe/Oslo		Atlantic/Jan_Mayen
+Link	Europe/Berlin		Atlantic/Jan_Mayen
+Link	Africa/Abidjan		Atlantic/St_Helena
 Link	Australia/Sydney	Australia/ACT
 Link	Australia/Sydney	Australia/Canberra
 Link	Australia/Hobart	Australia/Currie
@@ -81,7 +152,22 @@ Link	Africa/Cairo		Egypt
 Link	Europe/Dublin		Eire
 Link	Etc/UTC			Etc/UCT
 Link	Europe/London		Europe/Belfast
+Link	Europe/Prague		Europe/Bratislava
+Link	Europe/Zurich		Europe/Busingen
+Link	Europe/London		Europe/Guernsey
+Link	Europe/London		Europe/Isle_of_Man
+Link	Europe/London		Europe/Jersey
+Link	Europe/Belgrade		Europe/Ljubljana
+Link	Europe/Helsinki		Europe/Mariehamn
+Link	Asia/Nicosia		Europe/Nicosia
+Link	Europe/Belgrade		Europe/Podgorica
+Link	Europe/Rome		Europe/San_Marino
+Link	Europe/Belgrade		Europe/Sarajevo
+Link	Europe/Belgrade		Europe/Skopje
 Link	Europe/Chisinau		Europe/Tiraspol
+Link	Europe/Zurich		Europe/Vaduz
+Link	Europe/Rome		Europe/Vatican
+Link	Europe/Belgrade		Europe/Zagreb
 Link	Europe/London		GB
 Link	Europe/London		GB-Eire
 Link	Etc/GMT			GMT+0
@@ -90,6 +176,9 @@ Link	Etc/GMT			GMT0
 Link	Etc/GMT			Greenwich
 Link	Asia/Hong_Kong		Hongkong
 Link	Atlantic/Reykjavik	Iceland
+Link	Africa/Nairobi		Indian/Antananarivo
+Link	Africa/Nairobi		Indian/Comoro
+Link	Africa/Nairobi		Indian/Mayotte
 Link	Asia/Tehran		Iran
 Link	Asia/Jerusalem		Israel
 Link	America/Jamaica		Jamaica
@@ -103,8 +192,11 @@ Link	Pacific/Auckland	NZ
 Link	Pacific/Chatham		NZ-CHAT
 Link	America/Denver		Navajo
 Link	Asia/Shanghai		PRC
+Link	Pacific/Kanton		Pacific/Enderbury
 Link	Pacific/Honolulu	Pacific/Johnston
+Link	Pacific/Pago_Pago	Pacific/Midway
 Link	Pacific/Pohnpei		Pacific/Ponape
+Link	Pacific/Guam		Pacific/Saipan
 Link	Pacific/Pago_Pago	Pacific/Samoa
 Link	Pacific/Chuuk		Pacific/Truk
 Link	Pacific/Chuuk		Pacific/Yap
diff --git a/backzone b/backzone
index 3ce7277314c0..fc5e8bf7ac78 100644
--- a/backzone
+++ b/backzone
@@ -68,6 +68,91 @@
 #
 # As explained in the zic man page, the zone columns are:
 # Zone	NAME		STDOFF	RULES	FORMAT	[UNTIL]
+# and the rule columns are:
+# Rule	NAME	FROM	TO	-	IN	ON	AT	SAVE	LETTER/S
+
+
+# Ghana
+
+# From P Chan (2020-11-20):
+# Interpretation Amendment Ordinance, 1915 (No.24 of 1915) [1915-11-02]
+# Ordinances of the Gold Coast, Ashanti, Northern Territories 1915, p 69-71
+# https://books.google.com/books?id=ErA-AQAAIAAJ&pg=PA70
+# This Ordinance added "'Time' shall mean Greenwich Mean Time" to the
+# Interpretation Ordinance, 1876.
+#
+# Determination of the Time Ordinance, 1919 (No. 18 of 1919) [1919-11-24]
+# Ordinances of the Gold Coast, Ashanti, Northern Territories 1919, p 75-76
+# https://books.google.com/books?id=MbA-AQAAIAAJ&pg=PA75
+# This Ordinance removed the previous definition of time and introduced DST.
+#
+# Time Determination Ordinance (Cap. 214)
+# The Laws of the Gold Coast (including Togoland Under British Mandate)
+# Vol. II (1937), p 2328
+# https://books.google.com/books?id=Z7M-AQAAIAAJ&pg=PA2328
+# Revised edition of the 1919 Ordinance.
+#
+# Time Determination (Amendment) Ordinance, 1940 (No. 9 of 1940) [1940-04-06]
+# Annual Volume of the Laws of the Gold Coast:
+# Containing All Legislation Enacted During Year 1940, p 22
+# https://books.google.com/books?id=1ao-AQAAIAAJ&pg=PA22
+# This Ordinance changed the forward transition from September to May.
+#
+# Defence (Time Determination Ordinance Amendment) Regulations, 1942
+# (Regulations No. 6 of 1942) [1942-01-31, commenced on 1942-02-08]
+# Annual Volume of the Laws of the Gold Coast:
+# Containing All Legislation Enacted During Year 1942, p 48
+# https://books.google.com/books?id=Das-AQAAIAAJ&pg=PA48
+# These regulations advanced the [standard] time by thirty minutes.
+#
+# Defence (Time Determination Ordinance Amendment (No.2)) Regulations,
+# 1942 (Regulations No. 28 of 1942) [1942-04-25]
+# Annual Volume of the Laws of the Gold Coast:
+# Containing All Legislation Enacted During Year 1942, p 87
+# https://books.google.com/books?id=Das-AQAAIAAJ&pg=PA87
+# These regulations abolished DST and changed the time to GMT+0:30.
+#
+# Defence (Revocation) (No.4) Regulations, 1945 (Regulations No. 45 of
+# 1945) [1945-10-24, commenced on 1946-01-06]
+# Annual Volume of the Laws of the Gold Coast:
+# Containing All Legislation Enacted During Year 1945, p 256
+# https://books.google.com/books?id=9as-AQAAIAAJ&pg=PA256
+# These regulations revoked the previous two sets of Regulations.
+#
+# Time Determination (Amendment) Ordinance, 1945 (No. 18 of 1945) [1946-01-06]
+# Annual Volume of the Laws of the Gold Coast:
+# Containing All Legislation Enacted During Year 1945, p 69
+# https://books.google.com/books?id=9as-AQAAIAAJ&pg=PA69
+# This Ordinance abolished DST.
+#
+# Time Determination (Amendment) Ordinance, 1950 (No. 26 of 1950) [1950-07-22]
+# Annual Volume of the Laws of the Gold Coast:
+# Containing All Legislation Enacted During Year 1950, p 35
+# https://books.google.com/books?id=e60-AQAAIAAJ&pg=PA35
+# This Ordinance restored DST but with thirty minutes offset.
+#
+# Time Determination Ordinance (Cap. 264)
+# The Laws of the Gold Coast, Vol. V (1954), p 380
+# https://books.google.com/books?id=Mqc-AQAAIAAJ&pg=PA380
+# Revised edition of the Time Determination Ordinance.
+#
+# Time Determination (Amendment) Ordinance, 1956 (No. 21 of 1956) [1956-08-29]
+# Annual Volume of the Ordinances of the Gold Coast Enacted During the
+# Year 1956, p 83
+# https://books.google.com/books?id=VLE-AQAAIAAJ&pg=PA83
+# This Ordinance abolished DST.
+
+Rule	Ghana	1919	only	-	Nov	24	0:00	0:20	+0020
+Rule	Ghana	1920	1942	-	Jan	 1	2:00	0	GMT
+Rule	Ghana	1920	1939	-	Sep	 1	2:00	0:20	+0020
+Rule	Ghana	1940	1941	-	May	 1	2:00	0:20	+0020
+Rule	Ghana	1950	1955	-	Sep	 1	2:00	0:30	+0030
+Rule	Ghana	1951	1956	-	Jan	 1	2:00	0	GMT
+
+Zone	Africa/Accra	-0:00:52 -	LMT	1915 Nov  2
+			 0:00	Ghana	%s	1942 Feb  8
+			 0:30	-	+0030	1946 Jan  6
+			 0:00	Ghana	%s
 
 # Ethiopia
 # From Paul Eggert (2014-07-31):
@@ -101,14 +186,36 @@ Zone	Africa/Bamako	-0:32:00 -	LMT	1912
 Zone	Africa/Bangui	1:14:20	-	LMT	1912
 			1:00	-	WAT
 
-# Gambia
+# The Gambia
+# From P Chan (2020-12-09):
+# Standard time of GMT-1 was adopted on 1933-04-01.  On 1942-02-01, GMT was
+# adopted as a war time measure.  This was made permanent in 1946.
+#
+# Interpretation Ordinance, 1914 (No. 12 of 1914) [1914-09-29]
+# Interpretation Ordinance, 1933 (No. 10 of 1933) [1933-03-31]
+# Notice No. 5 of 1942, Colony of the Gambia Government Gazette, Vol. LIX,
+# No.2, 1942-01-15, p 2
+# Interpretation (Amendment) Ordinance, 1946 (No. 3 of 1946) [1946-07-15]
 Zone	Africa/Banjul	-1:06:36 -	LMT	1912
-			-1:06:36 -	BMT	1935 # Banjul Mean Time
-			-1:00	-	-01	1964
+			-1:06:36 -	BMT	1933 Apr  1 # Banjul Mean Time
+			-1:00	-	-01	1942 Feb  1  0:00
 			 0:00	-	GMT
 
 # Malawi
-Zone	Africa/Blantyre	2:20:00 -	LMT	1903 Mar
+# From P Chan (2020-12-09):
+# In 1911, Zomba mean time was adopted as the legal time of Nyasaland.  In
+# 1914, Zomba mean time switched from GMT+2:21:10 to GMT+2:21. On 1925-07-01,
+# GMT+2 was adopted.
+#
+# Interpretation and General Clauses Ordinance, 1911 (No. 12 of 1911)
+# [1911-07-24]
+# Notice No. 124 of 1914, 1914-06-30, The Nyasaland Government Gazette, Vol.
+# XXI, No. 8, 1914-06-30, p 122
+# Interpretation and General Clauses (Amendment) Ordinance, 1925 (No. 3 of
+# 1925) [1925-04-02]
+Zone	Africa/Blantyre	2:20:00 -	LMT	1911 Jul 24
+			2:21:10	-	ZMT	1914 Jun 30 # Zomba Mean Time
+			2:21	-	ZMT	1925 Jul  1
 			2:00	-	CAT
 
 # Republic of the Congo
@@ -145,19 +252,48 @@ Zone	Africa/Djibouti	2:52:36 -	LMT	1911 Jul
 Zone	Africa/Douala	0:38:48	-	LMT	1912
 			1:00	-	WAT
 # Sierra Leone
-# From Paul Eggert (2014-08-12):
-# The following table is from Shanks & Pottenger, but it can't be right.
-# Whitman gives Mar 31 - Aug 31 for 1931 on.
-# The International Hydrographic Bulletin, 1932-33, p 63 says that
-# Sierra Leone would advance its clocks by 20 minutes on 1933-10-01.
-# Rule	NAME	FROM	TO	-	IN	ON	AT	SAVE	LETTER/S
-Rule	SL	1935	1942	-	Jun	 1	0:00	0:40	-0020
-Rule	SL	1935	1942	-	Oct	 1	0:00	0	-01
-Rule	SL	1957	1962	-	Jun	 1	0:00	1:00	+01
-Rule	SL	1957	1962	-	Sep	 1	0:00	0	GMT
+# From P Chan (2020-12-09):
+# Standard time of GMT-1 was adopted on 1913-07-01.  Twenty minutes of DST was
+# introduce[d] in 1932 and was suspended in 1939.  In 1941, GMT was adopted by
+# Defence Regulations.  This was made permanent in 1946.
+#
+# Government Notice No. 121 of 1913, 1913-06-06, Sierra Leone Royal Gazette,
+# Vol. XLIV, No. 1384, 1913-06-14, p 347
+# Alteration of Time Ordinance, 1932 (No. 34 of 1932) [1932-12-01]
+# Alteration of Time (Amendment) Ordinance, 1938 (No. 25 of 1938) [1938-11-24]
+# Defence Regulations (No. 9), 1939 (Regulations No. 9 of 1939), 1939-09-05
+# Defence Regulations (No. 11), 1939 (Regulations No. 11 of 1939), 1939-09-27
+# Defence (Amendment) (No. 17) Regulations, 1941 (Public Notice No. 157 of
+# 1941), 1914-12-04
+# Alteration of Time (Amendment) Ordinance, 1946 (No. 2 of 1946) [1946-02-07]
+
+# From Tim Parenti (2021-03-02), per P Chan (2021-02-25):
+# For Sierra Leone in 1957-1962, the standard time was defined in the
+# Alteration of Time Ordinance, 1932 (as amended in 1946, renamed to Local Time
+# Ordinance in 1960 and Local Time Act in 1961). It was unamended throughout
+# that period.  See references to "Time" in the Alphabetical Index of the
+# Legislation in force on the 31st day of December,
+#   1957: https://books.google.com/books?id=lvQ-AQAAIAAJ&pg=RA2-PA49
+#   1958: https://books.google.com/books?id=4fQ-AQAAIAAJ&pg=RA2-PA50
+#   1959: https://books.google.com/books?id=p_U-AQAAIAAJ&pg=RA2-PA55
+#   1960: https://books.google.com/books?id=JPY-AQAAIAAJ&pg=RA3-PA37
+#   1961: https://books.google.com/books?id=7vY-AQAAIAAJ&pg=RA3-PA41
+#   1962: https://books.google.com/books?id=W_c-AQAAIAAJ&pg=RA3-PA44
+#   1963: https://books.google.com/books?id=9vk-AQAAIAAJ&pg=RA1-PA47
+#
+# Although Shanks & Pottenger had DST from Jun 1 00:00 to Sep 1 00:00 in this
+# period, many contemporaneous almanacs agree that it wasn't used:
+# https://mm.icann.org/pipermail/tz/2021-February/029866.html
+# Go with the above.
+
+Rule	SL	1932	only	-	Dec	 1	 0:00	0:20	-0040
+Rule	SL	1933	1938	-	Mar	31	24:00	0	-01
+Rule	SL	1933	1939	-	Aug	31	24:00	0:20	-0040
+Rule	SL	1939	only	-	May	31	24:00	0	-01
 Zone	Africa/Freetown	-0:53:00 -	LMT	1882
-			-0:53:00 -	FMT	1913 Jun # Freetown Mean Time
-			-1:00	SL	%s	1957
+			-0:53:00 -	FMT	1913 Jul  1 # Freetown MT
+			-1:00	SL	%s	1939 Sep  5
+			-1:00	-	-01	1941 Dec  6 24:00
 			 0:00	SL	GMT/+01
 
 # Botswana
@@ -298,6 +434,85 @@ Zone	America/Aruba	-4:40:24 -	LMT	1912 Feb 12 # Oranjestad
 			-4:30	-	-0430	1965
 			-4:00	-	AST
 
+# Atikokan, Ontario
+
+# From Paul Eggert (1997-10-17):
+# Mark Brader writes that an article in the 1997-10-14 Toronto Star
+# says that Atikokan, Ontario currently does not observe DST,
+# but will vote on 11-10 whether to use EST/EDT.
+# He also writes that the Ontario Time Act (1990, Chapter T.9)
+# http://www.gov.on.ca/MBS/english/publications/statregs/conttext.html
+# says that Ontario east of 90W uses EST/EDT, and west of 90W uses CST/CDT.
+# Officially Atikokan is therefore on CST/CDT, and most likely this report
+# concerns a non-official time observed as a matter of local practice.
+#
+# From Paul Eggert (2000-10-02):
+# Matthews and Vincent (1998) write that Atikokan, Pickle Lake, and
+# New Osnaburgh observe CST all year, that Big Trout Lake observes
+# CST/CDT, and that Upsala and Shebandowan observe EST/EDT, all in
+# violation of the official Ontario rules.
+#
+# From Paul Eggert (2006-07-09):
+# Chris Walton (2006-07-06) mentioned an article by Stephanie MacLellan in the
+# 2005-07-21 Chronicle-Journal, which said:
+#
+#	The clocks in Atikokan stay set on standard time year-round.
+#	This means they spend about half the time on central time and
+#	the other half on eastern time.
+#
+#	For the most part, the system works, Mayor Dennis Brown said.
+#
+#	"The majority of businesses in Atikokan deal more with Eastern
+#	Canada, but there are some that deal with Western Canada," he
+#	said.  "I don't see any changes happening here."
+#
+# Walton also writes "Supposedly Pickle Lake and Mishkeegogamang
+# [New Osnaburgh] follow the same practice."
+
+# From Garry McKinnon (2006-07-14) via Chris Walton:
+# I chatted with a member of my board who has an outstanding memory
+# and a long history in Atikokan (and in the telecom industry) and he
+# can say for certain that Atikokan has been practicing the current
+# time keeping since 1952, at least.
+
+# From Paul Eggert (2006-07-17):
+# Shanks & Pottenger say that Atikokan has agreed with Rainy River
+# ever since standard time was introduced, but the information from
+# McKinnon sounds more authoritative.  For now, assume that Atikokan
+# switched to EST immediately after WWII era daylight saving time
+# ended.  This matches the old (less-populous) America/Coral_Harbour
+# entry since our cutoff date of 1970, so we can move
+# America/Coral_Harbour to the 'backward' file.
+
+Zone America/Atikokan	-6:06:28 -	LMT	1895
+			-6:00	Canada	C%sT	1940 Sep 29
+			-6:00	1:00	CDT	1942 Feb  9  2:00s
+			-6:00	Canada	C%sT	1945 Sep 30  2:00
+			-5:00	-	EST
+
+# Quebec east of Natashquan
+
+# From Paul Eggert (2021-05-09):
+# H. David Matthews and Mary Vincent's map
+# "It's about TIME", _Canadian Geographic_ (September-October 1998)
+# http://www.canadiangeographic.ca/Magazine/SO98/alacarte.asp
+# says that Quebec east of the -63 meridian is supposed to observe
+# AST, but residents as far east as Natashquan use EST/EDT, and
+# residents east of Natashquan use AST.
+# The Quebec department of justice writes in
+# "The situation in Minganie and Basse-Côte-Nord"
+# https://www.justice.gouv.qc.ca/en/department/ministre/functions-and-responsabilities/legal-time-in-quebec/the-situation-in-minganie-and-basse-cote-nord/
+# that the coastal strip from just east of Natashquan to Blanc-Sablon
+# observes Atlantic standard time all year round.
+# This common practice was codified into law as of 2007; see Legal Time Act,
+# CQLR c T-5.1 <http://legisquebec.gouv.qc.ca/en/ShowDoc/cs/T-5.1>.
+# For lack of better info, guess this practice began around 1970, contra to
+# Shanks & Pottenger who have this region observing AST/ADT.
+
+Zone America/Blanc-Sablon -3:48:28 -	LMT	1884
+			-4:00	Canada	A%sT	1970
+			-4:00	-	AST
+
 # Cayman Is
 Zone	America/Cayman	-5:25:32 -	LMT	1890     # Georgetown
 			-5:07:10 -	KMT	1912 Feb # Kingston Mean Time
@@ -318,6 +533,85 @@ Zone America/Coral_Harbour -5:32:40 -	LMT	1884
 			-5:00	NT_YK	E%sT	1946
 			-5:00	-	EST
 
+# From Chris Walton (2011-12-01):
+# There are two areas within the Canadian province of British Columbia
+# that do not currently observe daylight saving:
+# a) The Creston Valley (includes the town of Creston and surrounding area)
+# b) The eastern half of the Peace River Regional District
+# (includes the cities of Dawson Creek and Fort St. John)
+
+# Earlier this year I stumbled across a detailed article about the time
+# keeping history of Creston; it was written by Tammy Hardwick who is the
+# manager of the Creston & District Museum. The article was written in May 2009.
+# http://www.ilovecreston.com/?p=articles&t=spec&ar=260
+# According to the article, Creston has not changed its clocks since June 1918.
+# i.e. Creston has been stuck on UT-7 for 93 years.
+# Dawson Creek, on the other hand, changed its clocks as recently as April 1972.
+
+# Unfortunately the exact date for the time change in June 1918 remains
+# unknown and will be difficult to ascertain.  I e-mailed Tammy a few months
+# ago to ask if Sunday June 2 was a reasonable guess.  She said it was just
+# as plausible as any other date (in June).  She also said that after writing
+# the article she had discovered another time change in 1916; this is the
+# subject of another article which she wrote in October 2010.
+# http://www.creston.museum.bc.ca/index.php?module=comments&uop=view_comment&cm+id=56
+
+# Here is a summary of the three clock change events in Creston's history:
+# 1. 1884 or 1885: adoption of Mountain Standard Time (GMT-7)
+# Exact date unknown
+# 2. Oct 1916: switch to Pacific Standard Time (GMT-8)
+# Exact date in October unknown; Sunday October 1 is a reasonable guess.
+# 3. June 1918: switch to Pacific Daylight Time (GMT-7)
+# Exact date in June unknown; Sunday June 2 is a reasonable guess.
+# note 1:
+# On Oct 27/1918 when daylight saving ended in the rest of Canada,
+# Creston did not change its clocks.
+# note 2:
+# During WWII when the Federal Government legislated a mandatory clock change,
+# Creston did not oblige.
+# note 3:
+# There is no guarantee that Creston will remain on Mountain Standard Time
+# (UTC-7) forever.
+# The subject was debated at least once this year by the town Council.
+# http://www.bclocalnews.com/kootenay_rockies/crestonvalleyadvance/news/116760809.html
+
+# During a period WWII, summer time (Daylight saying) was mandatory in Canada.
+# In Creston, that was handled by shifting the area to PST (-8:00) then applying
+# summer time to cause the offset to be -7:00, the same as it had been before
+# the change.  It can be argued that the timezone abbreviation during this
+# period should be PDT rather than MST, but that doesn't seem important enough
+# (to anyone) to further complicate the rules.
+
+# The transition dates (and times) are guesses.
+
+Zone America/Creston	-7:46:04 -	LMT	1884
+			-7:00	-	MST	1916 Oct 1
+			-8:00	-	PST	1918 Jun 2
+			-7:00	-	MST
+
+# Curaçao
+# Milne gives 4:35:46.9 for Curaçao mean time; round to nearest.
+#
+# From Paul Eggert (2006-03-22):
+# Shanks & Pottenger say that The Bottom and Philipsburg have been at
+# -4:00 since standard time was introduced on 1912-03-02; and that
+# Kralendijk and Rincon used Kralendijk Mean Time (-4:33:08) from
+# 1912-02-02 to 1965-01-01.  The former is dubious, since S&P also say
+# Saba Island has been like Curaçao.
+# This all predates our 1970 cutoff, though.
+#
+# By July 2007 Curaçao and St Maarten are planned to become
+# associated states within the Netherlands, much like Aruba;
+# Bonaire, Saba and St Eustatius would become directly part of the
+# Netherlands as Kingdom Islands.  This won't affect their time zones
+# though, as far as we know.
+#
+Zone	America/Curacao	-4:35:47 -	LMT	1912 Feb 12 # Willemstad
+			-4:30	-	-0430	1965
+			-4:00	-	AST
+Link	America/Curacao	America/Kralendijk
+Link	America/Curacao	America/Lower_Princes
+
 # Dominica
 Zone America/Dominica	-4:05:36 -	LMT	1911 Jul  1  0:01 # Roseau
 			-4:00	-	AST
@@ -340,6 +634,7 @@ Zone	America/Grenada	-4:07:00 -	LMT	1911 Jul # St George's
 Zone America/Guadeloupe	-4:06:08 -	LMT	1911 Jun  8 # Pointe-à-Pitre
 			-4:00	 -	AST
 
+
 # Canada
 #
 # From Paul Eggert (2015-03-24):
@@ -351,7 +646,6 @@ Zone America/Guadeloupe	-4:06:08 -	LMT	1911 Jun  8 # Pointe-à-Pitre
 # Pottenger data.  The post-1970 entries have been corrected, but the
 # pre-1970 entries are unchecked and probably have errors.
 #
-# Rule	NAME	FROM	TO	-	IN	ON	AT	SAVE	LETTER/S
 Rule	Mont	1917	only	-	Mar	25	2:00	1:00	D
 Rule	Mont	1917	only	-	Apr	24	0:00	0	S
 Rule	Mont	1919	only	-	Mar	31	2:30	1:00	D
@@ -387,6 +681,48 @@ Zone America/Montreal	-4:54:16 -	LMT	1884
 Zone America/Montserrat	-4:08:52 -	LMT	1911 Jul  1  0:01 # Cork Hill
 			-4:00	-	AST
 
+# The Bahamas
+#
+# For 1899 Milne gives -5:09:29.5; round that.
+#
+# From P Chan (2020-11-27, corrected on 2020-12-02):
+# There were two periods of DST observed in 1942-1945: 1942-05-01
+# midnight to 1944-12-31 midnight and 1945-02-01 to 1945-10-17 midnight.
+# "midnight" should mean 24:00 from the context.
+#
+# War Time Order 1942 [1942-05-01] and War Time (No. 2) Order 1942  [1942-09-29]
+# Appendix to the Statutes of 7 George VI. and the Year 1942. p 34, 43
+# https://books.google.com/books?id=5rlNAQAAIAAJ&pg=RA3-PA34
+# https://books.google.com/books?id=5rlNAQAAIAAJ&pg=RA3-PA43
+#
+# War Time Order 1943 [1943-03-31] and War Time Order 1944 [1943-12-29]
+# Appendix to the Statutes of 8 George VI. and the Year 1943. p 9-10, 28-29
+# https://books.google.com/books?id=5rlNAQAAIAAJ&pg=RA4-PA9
+# https://books.google.com/books?id=5rlNAQAAIAAJ&pg=RA4-PA28
+#
+# War Time Order 1945 [1945-01-31] and the Order which revoke War Time Order
+# 1945 [1945-10-16] Appendix to the Statutes of 9 George VI. and the Year
+# 1945. p 160, 247-248
+# https://books.google.com/books?id=5rlNAQAAIAAJ&pg=RA6-PA160
+# https://books.google.com/books?id=5rlNAQAAIAAJ&pg=RA6-PA247
+#
+# From Sue Williams (2006-12-07):
+# The Bahamas announced about a month ago that they plan to change their DST
+# rules to sync with the U.S. starting in 2007....
+# http://www.jonesbahamas.com/?c=45&a=10412
+
+Rule	Bahamas	1942	only	-	May	 1	24:00	1:00	W
+Rule	Bahamas	1944	only	-	Dec	31	24:00	0	S
+Rule	Bahamas	1945	only	-	Feb	 1	0:00	1:00	W
+Rule	Bahamas	1945	only	-	Aug	14	23:00u	1:00	P # Peace
+Rule	Bahamas	1945	only	-	Oct	17	24:00	0	S
+Rule	Bahamas	1964	1975	-	Oct	lastSun	2:00	0	S
+Rule	Bahamas	1964	1975	-	Apr	lastSun	2:00	1:00	D
+
+Zone	America/Nassau	-5:09:30 -	LMT	1912 Mar 2
+			-5:00	Bahamas	E%sT	1976
+			-5:00	US	E%sT
+
 # United States
 #
 # From Paul Eggert (2018-03-18):
@@ -411,6 +747,13 @@ Zone America/Montserrat	-4:08:52 -	LMT	1911 Jul  1  0:01 # Cork Hill
 # https://cdnc.ucr.edu/cgi-bin/cdnc?a=d&d=DS19470110
 # front page reports on end.
 
+# Trinidad and Tobago
+Zone America/Port_of_Spain -4:06:04 -	LMT	1912 Mar 2
+			-4:00	-	AST
+Link America/Port_of_Spain America/Marigot
+Link America/Port_of_Spain America/St_Barthelemy
+Link America/Port_of_Spain America/Virgin
+
 # Argentina
 # This entry was intended for the following areas, but has been superseded by
 # more detailed zones.
@@ -434,7 +777,7 @@ Zone America/St_Lucia	-4:04:00 -	LMT	1890 # Castries
 			-4:04:00 -	CMT	1912 # Castries Mean Time
 			-4:00	-	AST
 
-# Virgin Is
+# US Virgin Is
 Zone America/St_Thomas	-4:19:44 -	LMT	1911 Jul # Charlotte Amalie
 			-4:00	-	AST
 
@@ -447,11 +790,36 @@ Zone America/St_Vincent	-4:04:56 -	LMT	1890 # Kingstown
 Zone America/Tortola	-4:18:28 -	LMT	1911 Jul # Road Town
 			-4:00	-	AST
 
+# Dumont d'Urville, Île des Pétrels, -6640+14001, since 1956-11
+# <https://en.wikipedia.org/wiki/Dumont_d'Urville_Station> (2005-12-05)
+#
+# Another base at Port-Martin, 50km east, began operation in 1947.
+# It was destroyed by fire on 1952-01-14.
+#
+Zone Antarctica/DumontDUrville 0 -	-00	1947
+			10:00	-	+10	1952 Jan 14
+			0	-	-00	1956 Nov
+			10:00	-	+10
+
 # McMurdo, Ross Island, since 1955-12
 Zone Antarctica/McMurdo	0	-	-00	1956
 			12:00	NZ	NZ%sT
 Link Antarctica/McMurdo Antarctica/South_Pole
 
+# Syowa, Antarctica
+#
+# From Hideyuki Suzuki (1999-02-06):
+# In all Japanese stations, +0300 is used as the standard time.
+#
+# Syowa station, which is the first antarctic station of Japan,
+# was established on 1957-01-29.  Since Syowa station is still the main
+# station of Japan, it's appropriate for the principal location.
+Zone Antarctica/Syowa	0	-	-00	1957 Jan 29
+			3:00	-	+03
+# See:
+# NIPR Antarctic Research Activities (1999-08-17)
+# http://www.nipr.ac.jp/english/ara01.html
+
 # Yemen
 # Milne says 2:59:54 was the meridian of the saluting battery at Aden,
 # and that Yemen was at 1:55:56, the meridian of the Hagia Sophia.
@@ -711,6 +1079,8 @@ Zone	Europe/Skopje	1:25:44	-	LMT	1884
 			1:00	-	CET	1982 Nov 27
 			1:00	EU	CE%sT
 
+
+
 # Moldova / Transnistria
 Zone	Europe/Tiraspol	1:58:32	-	LMT	1880
 			1:55	-	CMT	1918 Feb 15 # Chisinau MT
@@ -749,10 +1119,22 @@ Zone	Indian/Comoro	2:53:04 -	LMT	1911 Jul # Moroni, Gran Comoro
 Zone	Indian/Mayotte	3:00:56 -	LMT	1911 Jul # Mamoutzou
 			3:00	-	EAT
 
-# US minor outlying islands
+# Phoenix Islands, Kiribati
+# From Paul Eggert (2021-05-27):
+# Enderbury was inhabited 1860/1880s to mine guano, and 1938-03-06/1942-02-09
+# for aviation (ostensibly commercial, but military uses foreseen).
+# The 19th-century dates are approximate.  See Pacific/Kanton for
+# the currently-inhabited representative for this timezone.
+Zone Pacific/Enderbury	0	-	-00	1860
+			-11:24:20 -	LMT	1885
+			0	-	-00	1938 Mar  6
+			-12:00	-	-12	1942 Feb  9
+			0	-	-00
+
+# Johnston
 Zone Pacific/Johnston	-10:00	-	HST
 
-# US minor outlying islands
+# Midway
 #
 # From Mark Brader (2005-01-23):
 # [Fallacies and Fantasies of Air Transport History, by R.E.G. Davies,
@@ -775,3 +1157,7 @@ Zone Pacific/Saipan	-14:17:00 -	LMT	1844 Dec 31
 			 9:00	-	+09	1969 Oct
 			10:00	-	+10	2000 Dec 23
 			10:00	-	ChST	# Chamorro Standard Time
+
+# Local Variables:
+# coding: utf-8
+# End:
diff --git a/checktab.awk b/checktab.awk
index ec145b5adf95..23e0a3a5c567 100644
--- a/checktab.awk
+++ b/checktab.awk
@@ -58,11 +58,12 @@ BEGIN {
 				zone_table, zone_NR >>"/dev/stderr"
 			status = 1
 		}
-		split($1, cca, /,/)
-		cc = cca[1]
+		ccs = input_ccs[zone_NR] = $1
 		coordinates = $2
 		tz = $3
-		comments = $4
+		comments = input_comments[zone_NR] = $4
+		split(ccs, cca, /,/)
+		cc = cca[1]
 
 		# Don't complain about a special case for Crimea in zone.tab.
 		# FIXME: zone.tab should be removed, since it is obsolete.
@@ -77,12 +78,9 @@ BEGIN {
 		cc0 = cc
 		tz0 = tz
 		tztab[tz] = 1
-		tz2comments[tz] = comments
 		tz2NR[tz] = zone_NR
 		for (i in cca) {
 		    cc = cca[i]
-		    cctz = cc tz
-		    cctztab[cctz] = 1
 		    if (cc2name[cc]) {
 			cc_used[cc]++
 		    } else {
@@ -99,27 +97,27 @@ BEGIN {
 		}
 	}
 
-	for (cctz in cctztab) {
-		cc = substr (cctz, 1, 2)
-		tz = substr (cctz, 3)
-		if (1 < cc_used[cc]) {
-			comments_needed[tz] = cc
-		}
-	}
-	for (cctz in cctztab) {
-	  cc = substr (cctz, 1, 2)
-	  tz = substr (cctz, 3)
-	  if (!comments_needed[tz] && tz2comments[tz]) {
+	for (i = 1; i <= zone_NR; i++) {
+	  ccs = input_ccs[i]
+	  if (!ccs) continue
+	  comments = input_comments[i]
+	  split(ccs, cca, /,/)
+	  used_max = 0
+          for (j in cca) {
+	    cc = cca[j]
+	    if (used_max < cc_used[cc]) {
+	      used_max = cc_used[cc]
+	    }
+	  }
+	  if (used_max <= 1 && comments) {
 	    printf "%s:%d: unnecessary comment '%s'\n", \
-		zone_table, tz2NR[tz], tz2comments[tz] \
-		>>"/dev/stderr"
-	    tz2comments[tz] = 0
+	      zone_table, i, comments \
+	      >>"/dev/stderr"
 	    status = 1
-	  } else if (comments_needed[tz] && !tz2comments[tz]) {
+	  } else if (1 < cc_used[cc] && !comments) {
 	    printf "%s:%d: missing comment for %s\n", \
-	      zone_table, tz2NR[tz], comments_needed[tz] \
+	      zone_table, i, cc \
 	      >>"/dev/stderr"
-	    tz2comments[tz] = 1
 	    status = 1
 	  }
 	}
@@ -149,8 +147,8 @@ $1 ~ /^#/ { next }
 		ruleUsed[$2] = 1
 		if ($3 ~ /%/) rulePercentUsed[$2] = 1
 	}
-	if (tz && tz ~ /\//) {
-		if (!tztab[tz]) {
+	if (tz && tz ~ /\// && tz !~ /^Etc\//) {
+		if (!tztab[tz] && FILENAME != "backward") {
 			printf "%s: no data for '%s'\n", zone_table, tz \
 				>>"/dev/stderr"
 			status = 1
@@ -173,7 +171,7 @@ END {
 		}
 	}
 	for (tz in tztab) {
-		if (!zoneSeen[tz]) {
+		if (!zoneSeen[tz] && tz !~ /^Etc\//) {
 			printf "%s:%d: no Zone table for '%s'\n", \
 				zone_table, tz2NR[tz], tz >>"/dev/stderr"
 			status = 1
diff --git a/europe b/europe
index bba4d5648228..1204c09d0abe 100644
--- a/europe
+++ b/europe
@@ -68,7 +68,6 @@
 #        0:00       GMT  BST  BDST  Greenwich, British Summer
 #        0:00       GMT  IST        Greenwich, Irish Summer
 #        0:00       WET  WEST WEMT  Western Europe
-#        0:19:32.13 AMT* NST*       Amsterdam, Netherlands Summer (1835-1937)
 #        1:00       BST             British Standard (1968-1971)
 #        1:00       IST  GMT        Irish Standard (1968-) with winter DST
 #        1:00       CET  CEST CEMT  Central Europe
@@ -506,9 +505,6 @@ Zone	Europe/London	-0:01:15 -	LMT	1847 Dec  1  0:00s
 			 1:00	-	BST	1971 Oct 31  2:00u
 			 0:00	GB-Eire	%s	1996
 			 0:00	EU	GMT/BST
-Link	Europe/London	Europe/Jersey
-Link	Europe/London	Europe/Guernsey
-Link	Europe/London	Europe/Isle_of_Man
 
 # From Paul Eggert (2018-02-15):
 # In January 2018 we discovered that the negative SAVE values in the
@@ -1307,9 +1303,8 @@ Zone	Europe/Helsinki	1:39:49 -	LMT	1878 May 31
 			1:39:49	-	HMT	1921 May    # Helsinki Mean Time
 			2:00	Finland	EE%sT	1983
 			2:00	EU	EE%sT
-
 # Åland Is
-Link	Europe/Helsinki	Europe/Mariehamn
+# See Europe/Helsinki.
 
 
 # France
@@ -1505,8 +1500,7 @@ Zone	Europe/Berlin	0:53:28 -	LMT	1893 Apr
 
 # From Arthur David Olson (2012-03-03):
 # Büsingen and Zurich have shared clocks since 1970.
-
-Link	Europe/Zurich	Europe/Busingen
+# See Europe/Zurich.
 
 # Georgia
 # Please see the "asia" file for Asia/Tbilisi.
@@ -1800,8 +1794,9 @@ Zone	Europe/Rome	0:49:56 -	LMT	1866 Dec 12
 			1:00	Italy	CE%sT	1980
 			1:00	EU	CE%sT
 
-Link	Europe/Rome	Europe/Vatican
-Link	Europe/Rome	Europe/San_Marino
+# Kosovo
+# See Europe/Belgrade.
+
 
 # Latvia
 
@@ -1895,7 +1890,7 @@ Zone	Europe/Riga	1:36:34	-	LMT	1880
 # I could confirm from the paper that Liechtenstein did in fact follow
 # the same DST in 1941 and 1942 as Switzerland did.
 
-Link Europe/Zurich Europe/Vaduz
+# See Europe/Zurich.
 
 
 # Lithuania
@@ -2150,6 +2145,10 @@ Zone	Europe/Monaco	0:29:32 -	LMT	1892 Jun  1
 # The data entries before 1945 are taken from
 # https://www.staff.science.uu.nl/~gent0113/wettijd/wettijd.htm
 
+# From Paul Eggert (2021-05-09):
+# I invented the abbreviations AMT for Amsterdam Mean Time and NST for
+# Netherlands Summer Time, used in the Netherlands from 1835 to 1937.
+
 # Rule	NAME	FROM	TO	-	IN	ON	AT	SAVE	LETTER/S
 Rule	Neth	1916	only	-	May	 1	0:00	1:00	NST	# Netherlands Summer Time
 Rule	Neth	1916	only	-	Oct	 1	0:00	0	AMT	# Amsterdam Mean Time
@@ -2248,8 +2247,7 @@ Zone	Europe/Oslo	0:43:00 -	LMT	1895 Jan  1
 # Haudegen did not surrender to the Allies until September 1945.
 #
 # All these events predate our cutoff date of 1970, so use Europe/Oslo
-# for these regions.
-Link	Europe/Oslo	Arctic/Longyearbyen
+# for these regions; see 'backward'.
 
 # Poland
 
@@ -2376,12 +2374,10 @@ Rule	Port	1943	1945	-	Aug	Sat>=25	22:00s	1:00	S
 Rule	Port	1944	1945	-	Apr	Sat>=21	22:00s	2:00	M
 Rule	Port	1946	only	-	Apr	Sat>=1	23:00s	1:00	S
 Rule	Port	1946	only	-	Oct	Sat>=1	23:00s	0	-
-Rule	Port	1947	1949	-	Apr	Sun>=1	 2:00s	1:00	S
-Rule	Port	1947	1949	-	Oct	Sun>=1	 2:00s	0	-
-# Shanks & Pottenger say DST was observed in 1950; go with Whitman.
+# Whitman says DST was not observed in 1950; go with Shanks & Pottenger.
 # Whitman gives Oct lastSun for 1952 on; go with Shanks & Pottenger.
-Rule	Port	1951	1965	-	Apr	Sun>=1	 2:00s	1:00	S
-Rule	Port	1951	1965	-	Oct	Sun>=1	 2:00s	0	-
+Rule	Port	1947	1965	-	Apr	Sun>=1	 2:00s	1:00	S
+Rule	Port	1947	1965	-	Oct	Sun>=1	 2:00s	0	-
 Rule	Port	1977	only	-	Mar	27	 0:00s	1:00	S
 Rule	Port	1977	only	-	Sep	25	 0:00s	0	-
 Rule	Port	1978	1979	-	Apr	Sun>=1	 0:00s	1:00	S
@@ -3520,14 +3516,9 @@ Zone	Europe/Belgrade	1:22:00	-	LMT	1884
 # Shanks & Pottenger don't give as much detail, so go with Koželj.
 			1:00	-	CET	1982 Nov 27
 			1:00	EU	CE%sT
-Link Europe/Belgrade Europe/Ljubljana	# Slovenia
-Link Europe/Belgrade Europe/Podgorica	# Montenegro
-Link Europe/Belgrade Europe/Sarajevo	# Bosnia and Herzegovina
-Link Europe/Belgrade Europe/Skopje	# North Macedonia
-Link Europe/Belgrade Europe/Zagreb	# Croatia
 
 # Slovakia
-Link Europe/Prague Europe/Bratislava
+# See Europe/Prague.
 
 # Slovenia
 # See Europe/Belgrade.
@@ -3683,6 +3674,9 @@ Zone	Atlantic/Canary	-1:01:36 -	LMT	1922 Mar # Las Palmas de Gran C.
 #
 # Source: The newspaper "Dagens Nyheter", 1916-10-01, page 7 upper left.
 
+# An extra-special abbreviation style is SET for Swedish Time (svensk
+# normaltid) 1879-1899, 3° west of the Stockholm Observatory.
+
 # Zone	NAME		STDOFF	RULES	FORMAT	[UNTIL]
 Zone Europe/Stockholm	1:12:12 -	LMT	1879 Jan  1
 			1:00:14	-	SET	1900 Jan  1 # Swedish Time
@@ -3995,7 +3989,7 @@ Zone	Europe/Istanbul	1:55:52 -	LMT	1880
 			2:00	1:00	EEST	2015 Nov  8  1:00u
 			2:00	EU	EE%sT	2016 Sep  7
 			3:00	-	+03
-Link	Europe/Istanbul	Asia/Istanbul	# Istanbul is in both continents.
+# See the 'backward' file for Asia/Istanbul.
 
 # Ukraine
 #
diff --git a/leap-seconds.list b/leap-seconds.list
index 3198d65146a5..cfda3e885e64 100644
--- a/leap-seconds.list
+++ b/leap-seconds.list
@@ -204,10 +204,10 @@
 #	current -- the update time stamp, the data and the name of the file
 #	will not change.
 #
-#	Updated through IERS Bulletin C61
-#	File expires on:  28 December 2021
+#	Updated through IERS Bulletin C62
+#	File expires on:  28 June 2022
 #
-#@	3849638400
+#@	3865363200
 #
 2272060800	10	# 1 Jan 1972
 2287785600	11	# 1 Jul 1972
@@ -252,4 +252,4 @@
 #	the hash line is also ignored in the
 #	computation.
 #
-#h 	2ab8253d d4380d28 75f01343 381504f8 8f8a4bfc
+#h 	599d45bf accd4b4f 8b60e46 49b623 7d13b825
diff --git a/leapseconds b/leapseconds
index cf0df04c3c8e..834b96ea882c 100644
--- a/leapseconds
+++ b/leapseconds
@@ -72,11 +72,11 @@ Leap	2016	Dec	31	23:59:60	+	S
 # Any additional leap seconds will come after this.
 # This Expires line is commented out for now,
 # so that pre-2020a zic implementations do not reject this file.
-#Expires 2021	Dec	28	00:00:00
+#Expires 2022	Jun	28	00:00:00
 
 # POSIX timestamps for the data in this file:
 #updated 1467936000 (2016-07-08 00:00:00 UTC)
-#expires 1640649600 (2021-12-28 00:00:00 UTC)
+#expires 1656374400 (2022-06-28 00:00:00 UTC)
 
-#	Updated through IERS Bulletin C61
-#	File expires on:  28 December 2021
+#	Updated through IERS Bulletin C62
+#	File expires on:  28 June 2022
diff --git a/northamerica b/northamerica
index ddc575976e59..a2f2b43c6f24 100644
--- a/northamerica
+++ b/northamerica
@@ -729,7 +729,11 @@ Zone America/Adak	 12:13:22 -	LMT	1867 Oct 19 12:44:35
 			-11:00	US	B%sT	1983 Oct 30  2:00
 			-10:00	US	AH%sT	1983 Nov 30
 			-10:00	US	H%sT
-# The following switches don't quite make our 1970 cutoff.
+# The following switches don't make our 1970 cutoff.
+#
+# Kiska observed Tokyo date and time during Japanese occupation from
+# 1942-06-06 to 1943-07-29, and similarly for Attu from 1942-06-07 to
+# 1943-05-29 (all dates American).  Both islands are now uninhabited.
 #
 # Shanks writes that part of southwest Alaska (e.g. Aniak)
 # switched from -11:00 to -10:00 on 1968-09-22 at 02:00,
@@ -1593,24 +1597,7 @@ Zone America/Moncton	-4:19:08 -	LMT	1883 Dec  9
 # From Paul Eggert (2020-01-10):
 # See America/Toronto for most of Quebec, including Montreal.
 # See America/Halifax for the Îles de la Madeleine and the Listuguj reserve.
-#
-# Matthews and Vincent (1998) also write that Quebec east of the -63
-# meridian is supposed to observe AST, but residents as far east as
-# Natashquan use EST/EDT, and residents east of Natashquan use AST.
-# The Quebec department of justice writes in
-# "The situation in Minganie and Basse-Côte-Nord"
-# https://www.justice.gouv.qc.ca/en/department/ministre/functions-and-responsabilities/legal-time-in-quebec/the-situation-in-minganie-and-basse-cote-nord/
-# that the coastal strip from just east of Natashquan to Blanc-Sablon
-# observes Atlantic standard time all year round.
-# This common practice was codified into law as of 2007; see Legal Time Act,
-# CQLR c T-5.1 <http://legisquebec.gouv.qc.ca/en/ShowDoc/cs/T-5.1>.
-# For lack of better info, guess this practice began around 1970, contra to
-# Shanks & Pottenger who have this region observing AST/ADT.
-
-# Zone	NAME		STDOFF	RULES	FORMAT	[UNTIL]
-Zone America/Blanc-Sablon -3:48:28 -	LMT	1884
-			-4:00	Canada	A%sT	1970
-			-4:00	-	AST
+# See America/Puerto_Rico for east of Natashquan.
 
 # Ontario
 
@@ -1649,54 +1636,6 @@ Zone America/Blanc-Sablon -3:48:28 -	LMT	1884
 # time became a comic failure in Orillia. Toronto Star 2017-07-08.
 # https://www.thestar.com/news/insight/2017/07/08/bold-attempt-at-daylight-saving-time-became-a-comic-failure-in-orillia.html
 
-# From Paul Eggert (1997-10-17):
-# Mark Brader writes that an article in the 1997-10-14 Toronto Star
-# says that Atikokan, Ontario currently does not observe DST,
-# but will vote on 11-10 whether to use EST/EDT.
-# He also writes that the Ontario Time Act (1990, Chapter T.9)
-# http://www.gov.on.ca/MBS/english/publications/statregs/conttext.html
-# says that Ontario east of 90W uses EST/EDT, and west of 90W uses CST/CDT.
-# Officially Atikokan is therefore on CST/CDT, and most likely this report
-# concerns a non-official time observed as a matter of local practice.
-#
-# From Paul Eggert (2000-10-02):
-# Matthews and Vincent (1998) write that Atikokan, Pickle Lake, and
-# New Osnaburgh observe CST all year, that Big Trout Lake observes
-# CST/CDT, and that Upsala and Shebandowan observe EST/EDT, all in
-# violation of the official Ontario rules.
-#
-# From Paul Eggert (2006-07-09):
-# Chris Walton (2006-07-06) mentioned an article by Stephanie MacLellan in the
-# 2005-07-21 Chronicle-Journal, which said:
-#
-#	The clocks in Atikokan stay set on standard time year-round.
-#	This means they spend about half the time on central time and
-#	the other half on eastern time.
-#
-#	For the most part, the system works, Mayor Dennis Brown said.
-#
-#	"The majority of businesses in Atikokan deal more with Eastern
-#	Canada, but there are some that deal with Western Canada," he
-#	said.  "I don't see any changes happening here."
-#
-# Walton also writes "Supposedly Pickle Lake and Mishkeegogamang
-# [New Osnaburgh] follow the same practice."
-
-# From Garry McKinnon (2006-07-14) via Chris Walton:
-# I chatted with a member of my board who has an outstanding memory
-# and a long history in Atikokan (and in the telecom industry) and he
-# can say for certain that Atikokan has been practicing the current
-# time keeping since 1952, at least.
-
-# From Paul Eggert (2006-07-17):
-# Shanks & Pottenger say that Atikokan has agreed with Rainy River
-# ever since standard time was introduced, but the information from
-# McKinnon sounds more authoritative.  For now, assume that Atikokan
-# switched to EST immediately after WWII era daylight saving time
-# ended.  This matches the old (less-populous) America/Coral_Harbour
-# entry since our cutoff date of 1970, so we can move
-# America/Coral_Harbour to the 'backward' file.
-
 # From Mark Brader (2010-03-06):
 #
 # Currently the database has:
@@ -1842,11 +1781,7 @@ Zone America/Rainy_River -6:18:16 -	LMT	1895
 			-6:00	Canada	C%sT	1940 Sep 29
 			-6:00	1:00	CDT	1942 Feb  9  2:00s
 			-6:00	Canada	C%sT
-Zone America/Atikokan	-6:06:28 -	LMT	1895
-			-6:00	Canada	C%sT	1940 Sep 29
-			-6:00	1:00	CDT	1942 Feb  9  2:00s
-			-6:00	Canada	C%sT	1945 Sep 30  2:00
-			-5:00	-	EST
+# For Atikokan see America/Panama.
 
 
 # Manitoba
@@ -2037,60 +1972,6 @@ Zone America/Edmonton	-7:33:52 -	LMT	1906 Sep
 # Shanks & Pottenger write that since 1970 most of this region has
 # been like Vancouver.
 # Dawson Creek uses MST.  Much of east BC is like Edmonton.
-# Matthews and Vincent (1998) write that Creston is like Dawson Creek.
-
-# It seems though that (re: Creston) is not entirely correct:
-
-# From Chris Walton (2011-12-01):
-# There are two areas within the Canadian province of British Columbia
-# that do not currently observe daylight saving:
-# a) The Creston Valley (includes the town of Creston and surrounding area)
-# b) The eastern half of the Peace River Regional District
-# (includes the cities of Dawson Creek and Fort St. John)
-
-# Earlier this year I stumbled across a detailed article about the time
-# keeping history of Creston; it was written by Tammy Hardwick who is the
-# manager of the Creston & District Museum. The article was written in May 2009.
-# http://www.ilovecreston.com/?p=articles&t=spec&ar=260
-# According to the article, Creston has not changed its clocks since June 1918.
-# i.e. Creston has been stuck on UT-7 for 93 years.
-# Dawson Creek, on the other hand, changed its clocks as recently as April 1972.
-
-# Unfortunately the exact date for the time change in June 1918 remains
-# unknown and will be difficult to ascertain.  I e-mailed Tammy a few months
-# ago to ask if Sunday June 2 was a reasonable guess.  She said it was just
-# as plausible as any other date (in June).  She also said that after writing
-# the article she had discovered another time change in 1916; this is the
-# subject of another article which she wrote in October 2010.
-# http://www.creston.museum.bc.ca/index.php?module=comments&uop=view_comment&cm+id=56
-
-# Here is a summary of the three clock change events in Creston's history:
-# 1. 1884 or 1885: adoption of Mountain Standard Time (GMT-7)
-# Exact date unknown
-# 2. Oct 1916: switch to Pacific Standard Time (GMT-8)
-# Exact date in October unknown; Sunday October 1 is a reasonable guess.
-# 3. June 1918: switch to Pacific Daylight Time (GMT-7)
-# Exact date in June unknown; Sunday June 2 is a reasonable guess.
-# note 1:
-# On Oct 27/1918 when daylight saving ended in the rest of Canada,
-# Creston did not change its clocks.
-# note 2:
-# During WWII when the Federal Government legislated a mandatory clock change,
-# Creston did not oblige.
-# note 3:
-# There is no guarantee that Creston will remain on Mountain Standard Time
-# (UTC-7) forever.
-# The subject was debated at least once this year by the town Council.
-# http://www.bclocalnews.com/kootenay_rockies/crestonvalleyadvance/news/116760809.html
-
-# During a period WWII, summer time (Daylight saying) was mandatory in Canada.
-# In Creston, that was handled by shifting the area to PST (-8:00) then applying
-# summer time to cause the offset to be -7:00, the same as it had been before
-# the change.  It can be argued that the timezone abbreviation during this
-# period should be PDT rather than MST, but that doesn't seem important enough
-# (to anyone) to further complicate the rules.
-
-# The transition dates (and times) are guesses.
 
 # From Matt Johnson (2015-09-21):
 # Fort Nelson, BC, Canada will cancel DST this year.  So while previously they
@@ -2144,10 +2025,7 @@ Zone America/Fort_Nelson	-8:10:47 -	LMT	1884
 			-8:00	Vanc	P%sT	1987
 			-8:00	Canada	P%sT	2015 Mar  8  2:00
 			-7:00	-	MST
-Zone America/Creston	-7:46:04 -	LMT	1884
-			-7:00	-	MST	1916 Oct 1
-			-8:00	-	PST	1918 Jun 2
-			-7:00	-	MST
+# For Creston see America/Phoenix.
 
 # Northwest Territories, Nunavut, Yukon
 
@@ -2929,64 +2807,61 @@ Zone America/Tijuana	-7:48:04 -	LMT	1922 Jan  1  0:11:56
 
 # Anguilla
 # Antigua and Barbuda
-# See America/Port_of_Spain.
+# See America/Puerto_Rico.
 
-# Bahamas
-#
-# For 1899 Milne gives -5:09:29.5; round that.
-#
-# From P Chan (2020-11-27, corrected on 2020-12-02):
-# There were two periods of DST observed in 1942-1945: 1942-05-01
-# midnight to 1944-12-31 midnight and 1945-02-01 to 1945-10-17 midnight.
-# "midnight" should mean 24:00 from the context.
-#
-# War Time Order 1942 [1942-05-01] and War Time (No. 2) Order 1942  [1942-09-29]
-# Appendix to the Statutes of 7 George VI. and the Year 1942. p 34, 43
-# https://books.google.com/books?id=5rlNAQAAIAAJ&pg=RA3-PA34
-# https://books.google.com/books?id=5rlNAQAAIAAJ&pg=RA3-PA43
-#
-# War Time Order 1943 [1943-03-31] and War Time Order 1944 [1943-12-29]
-# Appendix to the Statutes of 8 George VI. and the Year 1943. p 9-10, 28-29
-# https://books.google.com/books?id=5rlNAQAAIAAJ&pg=RA4-PA9
-# https://books.google.com/books?id=5rlNAQAAIAAJ&pg=RA4-PA28
-#
-# War Time Order 1945 [1945-01-31] and the Order which revoke War Time Order
-# 1945 [1945-10-16] Appendix to the Statutes of 9 George VI. and the Year
-# 1945. p 160, 247-248
-# https://books.google.com/books?id=5rlNAQAAIAAJ&pg=RA6-PA160
-# https://books.google.com/books?id=5rlNAQAAIAAJ&pg=RA6-PA247
-#
-# From Sue Williams (2006-12-07):
-# The Bahamas announced about a month ago that they plan to change their DST
-# rules to sync with the U.S. starting in 2007....
-# http://www.jonesbahamas.com/?c=45&a=10412
+# The Bahamas
+# See America/Montreal.
 
-# Rule	NAME	FROM	TO	-	IN	ON	AT	SAVE	LETTER/S
-Rule	Bahamas	1942	only	-	May	 1	24:00	1:00	W
-Rule	Bahamas	1944	only	-	Dec	31	24:00	0	S
-Rule	Bahamas	1945	only	-	Feb	 1	0:00	1:00	W
-Rule	Bahamas	1945	only	-	Aug	14	23:00u	1:00	P # Peace
-Rule	Bahamas	1945	only	-	Oct	17	24:00	0	S
-Rule	Bahamas	1964	1975	-	Oct	lastSun	2:00	0	S
-Rule	Bahamas	1964	1975	-	Apr	lastSun	2:00	1:00	D
-# Zone	NAME		STDOFF	RULES	FORMAT	[UNTIL]
-Zone	America/Nassau	-5:09:30 -	LMT	1912 Mar 2
-			-5:00	Bahamas	E%sT	1976
-			-5:00	US	E%sT
 
 # Barbados
 
 # For 1899 Milne gives -3:58:29.2; round that.
 
+# From P Chan (2020-12-09 and 2020-12-11):
+# Standard time of GMT-4 was adopted in 1911.
+# Definition of Time Act, 1911 (1911-7) [1911-08-28]
+# 1912, Laws of Barbados (5 v.), OCLC Number: 919801291, Vol. 4, Image No. 522
+# 1944, Laws of Barbados (5 v.), OCLC Number: 84548697, Vol. 4, Image No. 122
+# http://llmc.com/browse.aspx?type=2&coll=85&div=297
+#
+# DST was observed in 1942-44.
+# Defence (Daylight Saving) Regulations, 1942, 1942-04-13
+# Defence (Daylight Saving) (Repeal) Regulations, 1942, 1942-08-22
+# Defence (Daylight Saving) Regulations, 1943, 1943-04-16
+# Defence (Daylight Saving) (Repeal) Regulations, 1943, 1943-09-01
+# Defence (Daylight Saving) Regulations, 1944, 1944-03-21
+# [Defence (Daylight Saving) (Amendment) Regulations 1944, 1944-03-28]
+# Defence (Daylight Saving) (Repeal) Regulations, 1944, 1944-08-30
+#
+# 1914-, Subsidiary Legis., Annual Vols. OCLC Number: 226290591
+# 1942: Image Nos. 527-528, 555-556
+# 1943: Image Nos. 178-179, 198
+# 1944: Image Nos. 113-115, 129
+# http://llmc.com/titledescfull.aspx?type=2&coll=85&div=297&set=98437
+#
+# From Tim Parenti (2021-02-20):
+# The transitions below are derived from P Chan's sources, except that the 1977
+# through 1980 transitions are from Shanks & Pottenger since we have no better
+# data there.  Of particular note, the 1944 DST regulation only advanced the
+# time to "exactly three and a half hours later than Greenwich mean time", as
+# opposed to "three hours" in the 1942 and 1943 regulations.
+
 # Rule	NAME	FROM	TO	-	IN	ON	AT	SAVE	LETTER/S
+Rule	Barb	1942	only	-	Apr	19	5:00u	1:00	D
+Rule	Barb	1942	only	-	Aug	31	6:00u	0	S
+Rule	Barb	1943	only	-	May	 2	5:00u	1:00	D
+Rule	Barb	1943	only	-	Sep	 5	6:00u	0	S
+Rule	Barb	1944	only	-	Apr	10	5:00u	0:30	-
+Rule	Barb	1944	only	-	Sep	10	6:00u	0	S
 Rule	Barb	1977	only	-	Jun	12	2:00	1:00	D
 Rule	Barb	1977	1978	-	Oct	Sun>=1	2:00	0	S
 Rule	Barb	1978	1980	-	Apr	Sun>=15	2:00	1:00	D
 Rule	Barb	1979	only	-	Sep	30	2:00	0	S
 Rule	Barb	1980	only	-	Sep	25	2:00	0	S
 # Zone	NAME		STDOFF	RULES	FORMAT	[UNTIL]
-Zone America/Barbados	-3:58:29 -	LMT	1924 # Bridgetown
-			-3:58:29 -	BMT	1932 # Bridgetown Mean Time
+Zone America/Barbados	-3:58:29 -	LMT	1911 Aug 28 # Bridgetown
+			-4:00	Barb	A%sT	1944
+			-4:00	Barb	AST/-0330 1945
 			-4:00	Barb	A%sT
 
 # Belize
@@ -3148,6 +3023,9 @@ Zone Atlantic/Bermuda	-4:19:18 -	LMT	1890	# Hamilton
 			-4:00	Canada	A%sT	1976
 			-4:00	US	A%sT
 
+# Caribbean Netherlands
+# See America/Puerto_Rico.
+
 # Cayman Is
 # See America/Panama.
 
@@ -3376,7 +3254,7 @@ Zone	America/Havana	-5:29:28 -	LMT	1890
 			-5:00	Cuba	C%sT
 
 # Dominica
-# See America/Port_of_Spain.
+# See America/Puerto_Rico.
 
 # Dominican Republic
 
@@ -3428,7 +3306,7 @@ Zone America/El_Salvador -5:56:48 -	LMT	1921 # San Salvador
 # Guadeloupe
 # St Barthélemy
 # St Martin (French part)
-# See America/Port_of_Spain.
+# See America/Puerto_Rico.
 
 # Guatemala
 #
@@ -3615,7 +3493,7 @@ Zone America/Martinique	-4:04:20 -      LMT	1890        # Fort-de-France
 			-4:00	-	AST
 
 # Montserrat
-# See America/Port_of_Spain.
+# See America/Puerto_Rico.
 
 # Nicaragua
 #
@@ -3687,7 +3565,6 @@ Zone	America/Managua	-5:45:08 -	LMT	1890
 Zone	America/Panama	-5:18:08 -	LMT	1890
 			-5:19:36 -	CMT	1908 Apr 22 # Colón Mean Time
 			-5:00	-	EST
-Link America/Panama America/Cayman
 
 # Puerto Rico
 # There are too many San Juans elsewhere, so we'll use 'Puerto_Rico'.
@@ -3699,7 +3576,7 @@ Zone America/Puerto_Rico -4:24:25 -	LMT	1899 Mar 28 12:00 # San Juan
 
 # St Kitts-Nevis
 # St Lucia
-# See America/Port_of_Spain.
+# See America/Puerto_Rico.
 
 # St Pierre and Miquelon
 # There are too many St Pierres elsewhere, so we'll use 'Miquelon'.
@@ -3710,7 +3587,10 @@ Zone America/Miquelon	-3:44:40 -	LMT	1911 May 15 # St Pierre
 			-3:00	Canada	-03/-02
 
 # St Vincent and the Grenadines
-# See America/Port_of_Spain.
+# See America/Puerto_Rico.
+
+# Sint Maarten
+# See America/Puerto_Rico.
 
 # Turks and Caicos
 #
@@ -3781,8 +3661,8 @@ Zone America/Grand_Turk	-4:44:32 -	LMT	1890
 			-5:00	US	E%sT
 
 # British Virgin Is
-# Virgin Is
-# See America/Port_of_Spain.
+# US Virgin Is
+# See America/Puerto_Rico.
 
 
 # Local Variables:
diff --git a/southamerica b/southamerica
index aad8b2dbd190..9d8f46039d3d 100644
--- a/southamerica
+++ b/southamerica
@@ -574,7 +574,7 @@ Zone America/Argentina/Ushuaia -4:33:12 - LMT	1894 Oct 31
 			-3:00	-	-03
 
 # Aruba
-Link America/Curacao America/Aruba
+# See America/Puerto_Rico.
 
 # Bolivia
 # Zone	NAME		STDOFF	RULES	FORMAT	[UNTIL]
@@ -1369,35 +1369,14 @@ Zone	America/Bogota	-4:56:16 -	LMT	1884 Mar 13
 # no information; probably like America/Bogota
 
 # Curaçao
-
-# Milne gives 4:35:46.9 for Curaçao mean time; round to nearest.
-#
-# From Paul Eggert (2006-03-22):
-# Shanks & Pottenger say that The Bottom and Philipsburg have been at
-# -4:00 since standard time was introduced on 1912-03-02; and that
-# Kralendijk and Rincon used Kralendijk Mean Time (-4:33:08) from
-# 1912-02-02 to 1965-01-01.  The former is dubious, since S&P also say
-# Saba Island has been like Curaçao.
-# This all predates our 1970 cutoff, though.
-#
-# By July 2007 Curaçao and St Maarten are planned to become
-# associated states within the Netherlands, much like Aruba;
-# Bonaire, Saba and St Eustatius would become directly part of the
-# Netherlands as Kingdom Islands.  This won't affect their time zones
-# though, as far as we know.
+# See America/Puerto_Rico.
 #
-# Zone	NAME		STDOFF	RULES	FORMAT	[UNTIL]
-Zone	America/Curacao	-4:35:47 -	LMT	1912 Feb 12 # Willemstad
-			-4:30	-	-0430	1965
-			-4:00	-	AST
-
 # From Arthur David Olson (2011-06-15):
 # use links for places with new iso3166 codes.
 # The name "Lower Prince's Quarter" is both longer than fourteen characters
-# and contains an apostrophe; use "Lower_Princes" below.
-
-Link	America/Curacao	America/Lower_Princes	# Sint Maarten
-Link	America/Curacao	America/Kralendijk	# Caribbean Netherlands
+# and contains an apostrophe; use "Lower_Princes"....
+# From Paul Eggert (2021-05-06):
+# These backward-compatibility links now are in the 'backward' file.
 
 # Ecuador
 #
@@ -1540,11 +1519,40 @@ Zone America/Cayenne	-3:29:20 -	LMT	1911 Jul
 			-3:00	-	-03
 
 # Guyana
+
+# From P Chan (2020-11-27):
+# https://books.google.com/books?id=5-5CAQAAMAAJ&pg=SA1-PA547
+# The Official Gazette of British Guiana. (New Series.) Vol. XL. July to
+# December, 1915, p 1547, lists as several notes:
+# "Local Mean Time 3 hours 52 mins. 39 secs. slow of Greenwich Mean Time
+# (Georgetown.) From 1st August, 1911, British Guiana Standard Mean Time 4
+# hours slow of Greenwich Mean Time, by notice in Official Gazette on 1st July,
+# 1911.  From 1st March, 1915, British Guiana Standard Mean Time 3 hours 45
+# mins. 0 secs. slow of Greenwich Mean Time, by notice in Official Gazette on
+# 23rd January, 1915."
+#
+# https://parliament.gov.gy/documents/acts/10923-act_no._27_of_1975_-_interpretation_and_general_clauses_(amendment)_act_1975.pdf
+# Interpretation and general clauses (Amendment) Act 1975 (Act No. 27 of 1975)
+# [dated 1975-07-31]
+# "This Act...shall come into operation on 1st August, 1975."
+# "...where any expression of time occurs...the time referred to shall signify
+# the standard time of Guyana which shall be three hours behind Greenwich Mean
+# Time."
+#
+# Circular No. 10/1992 dated 1992-03-20
+# https://dps.gov.gy/wp-content/uploads/2018/12/1992-03-20-Circular-010.pdf
+# "...cabinet has decided that with effect from Sunday 29th March, 1992, Guyana
+# Standard Time would be re-established at 01:00 hours by adjusting the hands
+# of the clock back to 24:00 hours."
+# Legislated in the Interpretation and general clauses (Amendment) Act 1992
+# (Act No. 6 of 1992) [passed 1992-03-27, published 1992-04-18]
+# https://parliament.gov.gy/documents/acts/5885-6_of_1992_interpretation_and_general_clauses_(amendment)_act_1992.pdf
+
 # Zone	NAME		STDOFF	RULES	FORMAT	[UNTIL]
-Zone	America/Guyana	-3:52:40 -	LMT	1915 Mar    # Georgetown
-			-3:45	-	-0345	1975 Jul 31
-			-3:00	-	-03	1991
-# IATA SSIM (1996-06) says -4:00.  Assume a 1991 switch.
+Zone	America/Guyana	-3:52:39 -	LMT	1911 Aug  1 # Georgetown
+			-4:00	-	-04	1915 Mar  1
+			-3:45	-	-0345	1975 Aug  1
+			-3:00	-	-03	1992 Mar 29  1:00
 			-4:00	-	-04
 
 # Paraguay
@@ -1685,24 +1693,7 @@ Zone America/Paramaribo	-3:40:40 -	LMT	1911
 			-3:00	-	-03
 
 # Trinidad and Tobago
-# Zone	NAME		STDOFF	RULES	FORMAT	[UNTIL]
-Zone America/Port_of_Spain -4:06:04 -	LMT	1912 Mar 2
-			-4:00	-	AST
-
-# These all agree with Trinidad and Tobago since 1970.
-Link America/Port_of_Spain America/Anguilla
-Link America/Port_of_Spain America/Antigua
-Link America/Port_of_Spain America/Dominica
-Link America/Port_of_Spain America/Grenada
-Link America/Port_of_Spain America/Guadeloupe
-Link America/Port_of_Spain America/Marigot	# St Martin (French part)
-Link America/Port_of_Spain America/Montserrat
-Link America/Port_of_Spain America/St_Barthelemy # St Barthélemy
-Link America/Port_of_Spain America/St_Kitts	# St Kitts & Nevis
-Link America/Port_of_Spain America/St_Lucia
-Link America/Port_of_Spain America/St_Thomas	# Virgin Islands (US)
-Link America/Port_of_Spain America/St_Vincent
-Link America/Port_of_Spain America/Tortola	# Virgin Islands (UK)
+# See America/Puerto_Rico.
 
 # Uruguay
 # From Paul Eggert (1993-11-18):
diff --git a/theory.html b/theory.html
index 28f6b8ec51a8..5a05f4b12d22 100644
--- a/theory.html
+++ b/theory.html
@@ -42,12 +42,13 @@ href="https://en.wikipedia.org/wiki/Unix_time">POSIX Epoch</a>
 (1970-01-01 00:00:00 <a
 href="https://en.wikipedia.org/wiki/Coordinated_Universal_Time"><abbr
 title="Coordinated Universal Time">UTC</abbr></a>).
-The database labels each timezone with a notable location and
-records all known clock transitions for that location.
 Although 1970 is a somewhat-arbitrary cutoff, there are significant
 challenges to moving the cutoff earlier even by a decade or two, due
 to the wide variety of local practices before computer timekeeping
 became prevalent.
+Most timezones correspond to a notable location and the database
+records all known clock transitions for that location;
+some timezones correspond instead to a fixed <abbr>UTC</abbr> offset.
 </p>
 
 <p>
@@ -58,8 +59,9 @@ specifies current standard time. For example, applications that deal
 with current and future timestamps in the traditional North
 American mountain time zone can choose from the timezones
 <code>America/Denver</code> which observes US-style daylight saving
-time, <code>America/Mazatlan</code> which observes Mexican-style DST,
-and <code>America/Phoenix</code> which does not observe DST.
+time (<abbr>DST</abbr>),
+<code>America/Mazatlan</code> which observes Mexican-style <abbr>DST</abbr>,
+and <code>America/Phoenix</code> which does not observe <abbr>DST</abbr>.
 Applications that also deal with past timestamps in the mountain time
 zone can choose from over a dozen timezones, such as
 <code>America/Boise</code>, <code>America/Edmonton</code>, and
@@ -68,7 +70,7 @@ time but differs from other timezones for some timestamps after 1970.
 </p>
 
 <p>
-Clock transitions before 1970 are recorded for each timezone,
+Clock transitions before 1970 are recorded for location-based timezones,
 because most systems support timestamps before 1970 and could
 misbehave if data entries were omitted for pre-1970 transitions.
 However, the database is not designed for and does not suffice for
@@ -190,8 +192,8 @@ in decreasing order of importance:
     <code>TZ</code> strings</a>.
     A file name component must not exceed 14 characters or start with
     '<code>-</code>'.
-    E.g., prefer <code>Asia/Brunei</code> to
-    <code>Asia/Bandar_Seri_Begawan</code>.
+    E.g., prefer <code>America/Noronha</code> to
+    <code>America/Fernando_de_Noronha</code>.
     Exceptions: see the discussion of legacy names below.
   </li>
   <li>
@@ -473,10 +475,10 @@ in decreasing order of importance:
 
     <p>
     <small>These abbreviations are:
-      AMT Amsterdam, Asunción, Athens;
+      AMT Asunción, Athens;
       BMT Baghdad, Bangkok, Batavia, Bermuda, Bern, Bogotá, Bridgetown,
         Brussels, Bucharest;
-      CMT Calamarca, Caracas, Chisinau, Colón, Copenhagen, Córdoba;
+      CMT Calamarca, Caracas, Chisinau, Colón, Córdoba;
       DMT Dublin/Dunsink;
       EMT Easter;
       FFMT Fort-de-France;
@@ -499,7 +501,8 @@ in decreasing order of importance:
       SMT Santiago, Simferopol, Singapore, Stanley;
       TBMT Tbilisi;
       TMT Tallinn, Tehran;
-      WMT Warsaw</small>.
+      WMT Warsaw;
+      ZMT Zomba.</small>
     </p>
 
     <p>
@@ -513,9 +516,7 @@ in decreasing order of importance:
 	1880&ndash;1916,
       MMT/MST/MDST for Moscow 1880&ndash;1919, and
       RMT/LST for Riga Mean Time and Latvian Summer time 1880&ndash;1926.
-    An extra-special case is SET for Swedish Time (<em>svensk
-    normaltid</em>) 1879&ndash;1899, 3&deg; west of the Stockholm
-    Observatory.</small>
+    </small>
     </p>
   </li>
   <li>
@@ -702,11 +703,9 @@ href="https://www.dissentmagazine.org/blog/booked-a-global-history-of-time-vanes
   <li>
     Sometimes historical timekeeping was specified more precisely
     than what the <code><abbr>tz</abbr></code> code can handle.
-    For example, from 1909 to 1937 <a
-    href="https://www.staff.science.uu.nl/~gent0113/wettijd/wettijd.htm"
-    hreflang="nl">Netherlands clocks</a> were legally Amsterdam Mean
+    For example, from 1880 to 1916 clocks in Ireland observed Dublin Mean
     Time (estimated to be <abbr>UT</abbr>
-    +00:19:32.13), but the <code><abbr>tz</abbr></code>
+    &minus;00:25:21.1), but the <code><abbr>tz</abbr></code>
     code cannot represent the fractional second.
     In practice these old specifications were rarely if ever
     implemented to subsecond precision.
@@ -753,7 +752,8 @@ href="https://www.dissentmagazine.org/blog/booked-a-global-history-of-time-vanes
     the Western 06:00 to be 12:00. These practices are largely outside
     the scope of the <code><abbr>tz</abbr></code> code and data, which
     provide only limited support for date and time localization
-    such as that required by POSIX. If DST is not used a different time zone
+    such as that required by POSIX.
+    If <abbr>DST</abbr> is not used a different time zone
     can often do the trick; for example, in Kenya a <code>TZ</code> setting
     like <code>&lt;-03&gt;3</code> or <code>America/Cayenne</code> starts
     the day six hours later than <code>Africa/Nairobi</code> does.
@@ -1271,7 +1271,8 @@ The directly-supported mechanism assumes that <code>time_t</code>
 counts of seconds since the POSIX epoch normally include leap seconds,
 as opposed to POSIX <code>time_t</code> counts which exclude leap seconds.
 This modified timescale is converted to <abbr>UTC</abbr>
-at the same point that time zone and DST adjustments are applied &ndash;
+at the same point that time zone and <abbr>DST</abbr>
+adjustments are applied &ndash;
 namely, at calls to <code>localtime</code> and analogous functions &ndash;
 and the process is driven by leap second information
 stored in alternate versions of the <abbr>TZif</abbr> files.
diff --git a/version b/version
index 1d590958afd8..ba5601efbeda 100644
--- a/version
+++ b/version
@@ -1 +1 @@
-2021a
+2021b
diff --git a/ziguard.awk b/ziguard.awk
index 7d6f7c99c952..6888c27156b9 100644
--- a/ziguard.awk
+++ b/ziguard.awk
@@ -114,15 +114,16 @@ DATAFORM != "main" {
   }
 }
 
-# If a Link line is followed by a Zone line for the same data, comment
+# If a Link line is followed by a Link or Zone line for the same data, comment
 # out the Link line.  This can happen if backzone overrides a Link
-# with a Zone.
-/^Link/ {
-  linkline[$3] = NR
-}
+# with a Zone or a different Link.
 /^Zone/ {
   sub(/^Link/, "#Link", line[linkline[$2]])
 }
+/^Link/ {
+  sub(/^Link/, "#Link", line[linkline[$3]])
+  linkline[$3] = NR
+}
 
 { line[NR] = $0 }
 
diff --git a/zone.tab b/zone.tab
index 1f0128f3b280..086458fb2073 100644
--- a/zone.tab
+++ b/zone.tab
@@ -3,7 +3,7 @@
 # This file is in the public domain, so clarified as of
 # 2009-05-17 by Arthur David Olson.
 #
-# From Paul Eggert (2018-06-27):
+# From Paul Eggert (2021-09-20):
 # This file is intended as a backward-compatibility aid for older programs.
 # New programs should use zone1970.tab.  This file is like zone1970.tab (see
 # zone1970.tab's comments), but with the following additional restrictions:
@@ -16,6 +16,9 @@
 # clocks have agreed since 1970; this is a narrower definition than
 # that of zone1970.tab.
 #
+# Unlike zone1970.tab, a row's third column can be a Link from
+# 'backward' instead of a Zone.
+#
 # This table is intended as an aid for users, to help them select timezones
 # appropriate for their practical needs.  It is not intended to take or
 # endorse any position on legal or territorial claims.
@@ -228,7 +231,7 @@ KE	-0117+03649	Africa/Nairobi
 KG	+4254+07436	Asia/Bishkek
 KH	+1133+10455	Asia/Phnom_Penh
 KI	+0125+17300	Pacific/Tarawa	Gilbert Islands
-KI	-0308-17105	Pacific/Enderbury	Phoenix Islands
+KI	-0247-17143	Pacific/Kanton	Phoenix Islands
 KI	+0152-15720	Pacific/Kiritimati	Line Islands
 KM	-1141+04316	Indian/Comoro
 KN	+1718-06243	America/St_Kitts
@@ -391,7 +394,7 @@ TK	-0922-17114	Pacific/Fakaofo
 TL	-0833+12535	Asia/Dili
 TM	+3757+05823	Asia/Ashgabat
 TN	+3648+01011	Africa/Tunis
-TO	-2110-17510	Pacific/Tongatapu
+TO	-210800-1751200	Pacific/Tongatapu
 TR	+4101+02858	Europe/Istanbul
 TT	+1039-06131	America/Port_of_Spain
 TV	-0831+17913	Pacific/Funafuti
diff --git a/zone1970.tab b/zone1970.tab
index 396e4d3810b1..c614be81f401 100644
--- a/zone1970.tab
+++ b/zone1970.tab
@@ -40,11 +40,9 @@ AL	+4120+01950	Europe/Tirane
 AM	+4011+04430	Asia/Yerevan
 AQ	-6617+11031	Antarctica/Casey	Casey
 AQ	-6835+07758	Antarctica/Davis	Davis
-AQ	-6640+14001	Antarctica/DumontDUrville	Dumont-d'Urville
 AQ	-6736+06253	Antarctica/Mawson	Mawson
 AQ	-6448-06406	Antarctica/Palmer	Palmer
 AQ	-6734-06808	Antarctica/Rothera	Rothera
-AQ	-690022+0393524	Antarctica/Syowa	Syowa
 AQ	-720041+0023206	Antarctica/Troll	Troll
 AQ	-7824+10654	Antarctica/Vostok	Vostok
 AR	-3436-05827	America/Argentina/Buenos_Aires	Buenos Aires (BA, CF)
@@ -97,7 +95,6 @@ BR	+0249-06040	America/Boa_Vista	Roraima
 BR	-0308-06001	America/Manaus	Amazonas (east)
 BR	-0640-06952	America/Eirunepe	Amazonas (west)
 BR	-0958-06748	America/Rio_Branco	Acre
-BS	+2505-07721	America/Nassau
 BT	+2728+08939	Asia/Thimphu
 BY	+5354+02734	Europe/Minsk
 BZ	+1730-08812	America/Belize
@@ -106,13 +103,11 @@ CA	+4439-06336	America/Halifax	Atlantic - NS (most areas); PE
 CA	+4612-05957	America/Glace_Bay	Atlantic - NS (Cape Breton)
 CA	+4606-06447	America/Moncton	Atlantic - New Brunswick
 CA	+5320-06025	America/Goose_Bay	Atlantic - Labrador (most areas)
-CA	+5125-05707	America/Blanc-Sablon	AST - QC (Lower North Shore)
-CA	+4339-07923	America/Toronto	Eastern - ON, QC (most areas)
+CA,BS	+4339-07923	America/Toronto	Eastern - ON, QC (most areas), Bahamas
 CA	+4901-08816	America/Nipigon	Eastern - ON, QC (no DST 1967-73)
 CA	+4823-08915	America/Thunder_Bay	Eastern - ON (Thunder Bay)
 CA	+6344-06828	America/Iqaluit	Eastern - NU (most east areas)
 CA	+6608-06544	America/Pangnirtung	Eastern - NU (Pangnirtung)
-CA	+484531-0913718	America/Atikokan	EST - ON (Atikokan); NU (Coral H)
 CA	+4953-09709	America/Winnipeg	Central - ON (west); Manitoba
 CA	+4843-09434	America/Rainy_River	Central - ON (Rainy R, Ft Frances)
 CA	+744144-0944945	America/Resolute	Central - NU (Resolute)
@@ -123,7 +118,6 @@ CA	+5333-11328	America/Edmonton	Mountain - AB; BC (E); SK (W)
 CA	+690650-1050310	America/Cambridge_Bay	Mountain - NU (west)
 CA	+6227-11421	America/Yellowknife	Mountain - NT (central)
 CA	+682059-1334300	America/Inuvik	Mountain - NT (west)
-CA	+4906-11631	America/Creston	MST - BC (Creston)
 CA	+5946-12014	America/Dawson_Creek	MST - BC (Dawson Cr, Ft St John)
 CA	+5848-12242	America/Fort_Nelson	MST - BC (Ft Nelson)
 CA	+6043-13503	America/Whitehorse	MST - Yukon (east)
@@ -131,7 +125,7 @@ CA	+6404-13925	America/Dawson	MST - Yukon (west)
 CA	+4916-12307	America/Vancouver	Pacific - BC (most areas)
 CC	-1210+09655	Indian/Cocos
 CH,DE,LI	+4723+00832	Europe/Zurich	Swiss time
-CI,BF,GM,GN,ML,MR,SH,SL,SN,TG	+0519-00402	Africa/Abidjan
+CI,BF,GH,GM,GN,ML,MR,SH,SL,SN,TG	+0519-00402	Africa/Abidjan
 CK	-2114-15946	Pacific/Rarotonga
 CL	-3327-07040	America/Santiago	Chile (most areas)
 CL	-5309-07055	America/Punta_Arenas	Region of Magallanes
@@ -142,7 +136,6 @@ CO	+0436-07405	America/Bogota
 CR	+0956-08405	America/Costa_Rica
 CU	+2308-08222	America/Havana
 CV	+1455-02331	Atlantic/Cape_Verde
-CW,AW,BQ,SX	+1211-06900	America/Curacao
 CX	-1025+10543	Indian/Christmas
 CY	+3510+03322	Asia/Nicosia	Cyprus (most areas)
 CY	+3507+03357	Asia/Famagusta	Northern Cyprus
@@ -170,7 +163,6 @@ FR	+4852+00220	Europe/Paris
 GB,GG,IM,JE	+513030-0000731	Europe/London
 GE	+4143+04449	Asia/Tbilisi
 GF	+0456-05220	America/Cayenne
-GH	+0533-00013	Africa/Accra
 GI	+3608-00521	Europe/Gibraltar
 GL	+6411-05144	America/Nuuk	Greenland (most areas)
 GL	+7646-01840	America/Danmarkshavn	National Park (east coast)
@@ -204,7 +196,7 @@ JP	+353916+1394441	Asia/Tokyo
 KE,DJ,ER,ET,KM,MG,SO,TZ,UG,YT	-0117+03649	Africa/Nairobi
 KG	+4254+07436	Asia/Bishkek
 KI	+0125+17300	Pacific/Tarawa	Gilbert Islands
-KI	-0308-17105	Pacific/Enderbury	Phoenix Islands
+KI	-0247-17143	Pacific/Kanton	Phoenix Islands
 KI	+0152-15720	Pacific/Kiritimati	Line Islands
 KP	+3901+12545	Asia/Pyongyang
 KR	+3733+12658	Asia/Seoul
@@ -262,19 +254,19 @@ NR	-0031+16655	Pacific/Nauru
 NU	-1901-16955	Pacific/Niue
 NZ,AQ	-3652+17446	Pacific/Auckland	New Zealand time
 NZ	-4357-17633	Pacific/Chatham	Chatham Islands
-PA,KY	+0858-07932	America/Panama
+PA,CA,KY	+0858-07932	America/Panama	EST - Panama, Cayman, ON (Atikokan), NU (Coral H)
 PE	-1203-07703	America/Lima
 PF	-1732-14934	Pacific/Tahiti	Society Islands
 PF	-0900-13930	Pacific/Marquesas	Marquesas Islands
 PF	-2308-13457	Pacific/Gambier	Gambier Islands
-PG	-0930+14710	Pacific/Port_Moresby	Papua New Guinea (most areas)
+PG,AQ	-0930+14710	Pacific/Port_Moresby	Papua New Guinea (most areas), Dumont d'Urville
 PG	-0613+15534	Pacific/Bougainville	Bougainville
 PH	+1435+12100	Asia/Manila
 PK	+2452+06703	Asia/Karachi
 PL	+5215+02100	Europe/Warsaw
 PM	+4703-05620	America/Miquelon
 PN	-2504-13005	Pacific/Pitcairn
-PR	+182806-0660622	America/Puerto_Rico
+PR,AG,CA,AI,AW,BL,BQ,CW,DM,GD,GP,KN,LC,MF,MS,SX,TT,VC,VG,VI	+182806-0660622	America/Puerto_Rico	AST
 PS	+3130+03428	Asia/Gaza	Gaza Strip
 PS	+313200+0350542	Asia/Hebron	West Bank
 PT	+3843-00908	Europe/Lisbon	Portugal (mainland)
@@ -314,12 +306,12 @@ RU	+4658+14242	Asia/Sakhalin	MSK+08 - Sakhalin Island
 RU	+6728+15343	Asia/Srednekolymsk	MSK+08 - Sakha (E); North Kuril Is
 RU	+5301+15839	Asia/Kamchatka	MSK+09 - Kamchatka
 RU	+6445+17729	Asia/Anadyr	MSK+09 - Bering Sea
-SA,KW,YE	+2438+04643	Asia/Riyadh
+SA,AQ,KW,YE	+2438+04643	Asia/Riyadh	Arabia, Syowa
 SB	-0932+16012	Pacific/Guadalcanal
 SC	-0440+05528	Indian/Mahe
 SD	+1536+03232	Africa/Khartoum
 SE	+5920+01803	Europe/Stockholm
-SG	+0117+10351	Asia/Singapore
+SG,MY	+0117+10351	Asia/Singapore	Singapore, peninsular Malaysia
 SR	+0550-05510	America/Paramaribo
 SS	+0451+03137	Africa/Juba
 ST	+0020+00644	Africa/Sao_Tome
@@ -334,9 +326,8 @@ TK	-0922-17114	Pacific/Fakaofo
 TL	-0833+12535	Asia/Dili
 TM	+3757+05823	Asia/Ashgabat
 TN	+3648+01011	Africa/Tunis
-TO	-2110-17510	Pacific/Tongatapu
+TO	-210800-1751200	Pacific/Tongatapu
 TR	+4101+02858	Europe/Istanbul
-TT,AG,AI,BL,DM,GD,GP,KN,LC,MF,MS,VC,VG,VI	+1039-06131	America/Port_of_Spain
 TV	-0831+17913	Pacific/Funafuti
 TW	+2503+12130	Asia/Taipei
 UA	+5026+03031	Europe/Kiev	Ukraine (most areas)
@@ -362,7 +353,7 @@ US	+465042-1012439	America/North_Dakota/New_Salem	Central - ND (Morton rural)
 US	+471551-1014640	America/North_Dakota/Beulah	Central - ND (Mercer)
 US	+394421-1045903	America/Denver	Mountain (most areas)
 US	+433649-1161209	America/Boise	Mountain - ID (south); OR (east)
-US	+332654-1120424	America/Phoenix	MST - Arizona (except Navajo)
+US,CA	+332654-1120424	America/Phoenix	MST - Arizona (except Navajo), Creston BC
 US	+340308-1181434	America/Los_Angeles	Pacific
 US	+611305-1495401	America/Anchorage	Alaska (most areas)
 US	+581807-1342511	America/Juneau	Alaska - Juneau area