[This is a repost with minor updates of <https://mm.icann.org/pipermail/tz/2024-March/058790.html>. This repost is in a separate email thread, with a clearer "Subject:" line.] The recent glitches with %z-related lines in the Portugal data lead me to think that it's time to start using %z in the main format. For example, instead of this:

# Zone NAME STDOFF RULES FORMAT [UNTIL] Zone Atlantic/Azores -1:42:40 - LMT 1884 # Ponta Delgada -1:54:32 - HMT 1912 Jan 1 2:00u # Horta MT -2:00 Port -02/-01 1942 Apr 25 22:00s -2:00 Port +00 1942 Aug 15 22:00s -2:00 Port -02/-01 1943 Apr 17 22:00s -2:00 Port +00 1943 Aug 28 22:00s -2:00 Port -02/-01 1944 Apr 22 22:00s -2:00 Port +00 1944 Aug 26 22:00s -2:00 Port -02/-01 1945 Apr 21 22:00s -2:00 Port +00 1945 Aug 25 22:00s -2:00 Port -02/-01 1966 Apr 3 2:00 -1:00 Port -01/+00 1983 Sep 25 1:00s -1:00 W-Eur -01/+00 1992 Sep 27 1:00s

the 'europe' file should contain this:

# Zone NAME STDOFF RULES FORMAT [UNTIL] Zone Atlantic/Azores -1:42:40 - LMT 1884 # Ponta Delgada -1:54:32 - HMT 1912 Jan 1 2:00u # Horta MT -2:00 Port %z 1966 Apr 3 2:00 -1:00 Port %z 1983 Sep 25 1:00s -1:00 W-Eur %z 1992 Sep 27 1:00s

This would eventually simplify future maintenance and help avoid similar glitches in the future. For now, the 'rearguard' format would continue to avoid %z in the FORMAT column. It's reasonable to use %z in 'europe' now, as zic has supported %z since release 2015f.