--- a/europe
+++ b/europe
@@ -957,23 +957,75 @@
 # A document of Government of Bulgaria (No. 94/1997) says:
 # EET -> EETDST is in 03:00 Local time in last Sunday of March ...
 # EETDST -> EET is in 04:00 Local time in last Sunday of October
+#
+# From Ivan Petrov Ivanov (2026-09-12):
+# Bulgarian summer time began in 1979 and every transition from 1979 to
+# 1996 was at midnight: clocks forward from 00:00 to 01:00, back from
+# 24:00 (Saturday) to 23:00.  Sources, all in Bulgarian:
+#
+# Decree 6/1979 (State Gazette 12/1979, p. 115): from 1979, clocks
+# forward "from 0:00 on 1 April" and back "on 1 October".  Railway and
+# BTA notices of 30-31 March and 27-28 September 1979 give the same
+# hours: "the new time from 00:00 on 1 April", "winter time from 0:00".
+#
+# 1980-1982: BTA notice of 1 April 1980 (Rabotnichesko Delo, Trud,
+# Narodna Mladezh, Narodna Armiya, Kooperativno Selo): summer time "from
+# 00:00 on 6 April, Sunday, to 24:00 on 27 September, Saturday".
+# Otechestven Front 1981-04-04: "on 4 April at midnight the clocks will
+# already show 1 ... on 26 September, Saturday, when at midnight the
+# clocks will be put back"; 1981-09-25: "on 26 September at 24:00".
+# Otechestven Front 1982-04-02: "on Saturday night, 3 to 4 April";
+# Narodna Mladezh 1982-09-23: "winter time from 24:00 on 25 September
+# 1982".  That is the first Sunday of April and the eve of the last
+# Sunday of September, at midnight.  The file's 23:00 springs, its
+# 01:00/02:00/03:00 autumns and its Monday 29 September 1980 have no
+# Bulgarian source.
+#
+# 1983-1996: Council of Ministers Decision 196 of 1982-12-28 set the
+# last Sunday of March and the last Saturday of September.  BTA notices
+# in Rabotnichesko Delo for every year 1983-1990 say "at 00:00" going
+# forward and "Saturday at 24:00" coming back: 1983-03-26, 1983-09-25,
+# 1984-03-25, 1984-09-06, 1985-03-30, 1985-09-28, 1986-03-29,
+# 1986-09-27, 1987-03-28, 1987-09-26, 1988-03-26, 1988-09-24,
+# 1989-03-25, 1989-09-05, 1990-03-24.  The yearly acts for 1991-1996
+# (Council of Ministers Decision 328/1991, Protocols 24/1992, 28/1993
+# and 86/1993, Decisions 112/1994, 118/1995, 205/1996) name Saturday
+# 24:00 or Sunday 00:00 every time.  In 1989 and 1995, when the last
+# Saturday of September is a week after the eve of the last Sunday, the
+# return was moved to the Sunday: BTA notice of 1989-09-05 ("on 24
+# September, Sunday, at 0:00"); Decision 394 of 1995-09-22 (State
+# Gazette 88/1995, "24:00 on 23 September 1995, Saturday").  So every
+# autumn 1983-1995 is the E-Eur instant; only the hour differs in
+# 1983-1990.
+#
+# 1996: Decision 205 of 1996-03-14 returned the clocks at 24:00 on
+# Saturday 28 September 1996 (Duma 1996-09-27, p. 1; Balkan Airlines in
+# Demokratsiya 1996-09-28, p. 7, counting the offset against Europe from
+# 29 September to 26 October inclusive).  Decree 94/1997 (State Gazette
+# 24/1997, p. 10) introduced the EU rules from 1997 and repealed Decree
+# 6/1979 and item 12 of Directive 15/1980.
+#
+# Before 1979 the entries are not changed; no Bulgarian source for
+# 1894, 1942 or 1945 has been read.
+#
+# Document images, transcriptions and the acts: https://oco.bg/tz/sofia
+# Deposit: https://doi.org/10.5281/zenodo.22727130 (all versions:
+# https://doi.org/10.5281/zenodo.22695588)
 #
 # Rule	NAME	FROM	TO	-	IN	ON	AT	SAVE	LETTER/S
-Rule	Bulg	1979	only	-	Mar	31	23:00	1:00	S
-Rule	Bulg	1979	only	-	Oct	 1	 1:00	0	-
-Rule	Bulg	1980	1982	-	Apr	Sat>=1	23:00	1:00	S
-Rule	Bulg	1980	only	-	Sep	29	 1:00	0	-
-Rule	Bulg	1981	only	-	Sep	27	 2:00	0	-
+Rule	Bulg	1979	only	-	Apr	 1	 0:00	1:00	S
+Rule	Bulg	1979	only	-	Oct	 1	 0:00	0	-
+Rule	Bulg	1980	1982	-	Apr	Sun>=1	 0:00	1:00	S
+Rule	Bulg	1980	1996	-	Sep	lastSun	 0:00	0	-
+Rule	Bulg	1983	1996	-	Mar	lastSun	 0:00	1:00	S
 # Zone	NAME		STDOFF	RULES	FORMAT	[UNTIL]
 Zone	Europe/Sofia	1:33:16 -	LMT	1880
 			1:56:56	-	IMT	1894 Nov 30 # Istanbul MT?
 			2:00	-	EET	1942 Nov  2  3:00
 			1:00	C-Eur	CE%sT	1945
 			1:00	-	CET	1945 Apr  2  3:00
-			2:00	-	EET	1979 Mar 31 23:00
-			2:00	Bulg	EE%sT	1982 Sep 26  3:00
-			2:00	C-Eur	EE%sT	1991
-			2:00	E-Eur	EE%sT	1997
+			2:00	-	EET	1979 Apr  1  0:00
+			2:00	Bulg	EE%sT	1997
 			2:00	EU	EE%sT
 
 # Cyprus