CLDR sets an assumption that name of zones are very stable. For example, "Pacific Standard Time" represents standard time used on US Pacific coast and the name itself does not change time to time.
Could you clarify how CLDR currently works for Ireland, without the proposed tzdb changes? tzdb's current data (which is the same as what it
was in 2017c) has three types of Irish timestamps that use the abbreviation "IST". The first type is for UT+00:34:39 and was observed in summer 1916; it has tm_isdst=1. The second type is for UT+01 and was observed in summers from 1922 through late 1940, then continuously until
late 1948, then in summers through 1968, and then in summers from 1972 through today; it also has tm_isdst=1. The third kind is also for UT+01 and was observed from late 1968 through late 1971; it has tm_isdst=0.
Are all three types of IST called "Irish Standard Time" in CLDR now? If not, then what does CLDR call them and how is this determined? And if so, we have a problem since the correct full name for IST is "Irish Summer Time" for timestamps before late 1968, and is "Irish Standard Time" for timestamps thereafter, and there's nothing in the tzdb data proper that specifies the transition date between the two full names.
CLDR does not have time zone names for dates before 1990. Historic zone names never used in a last few decades are not included. This is mainly because reducing overhead of managing localized names. Our primary focus is to provide good localized display names in modern software, not trying to provide every possible names historically used. CLDR suggests code implementators to use a UTC offset format as the fallback, for example, UTC+01:00 as the fallback when a name is not available. (CLDR also provides localized fallback format patterns in various locales). BTW, CLDR localized names are also based on ordinary people's expectation in each locale. For example, while people in Ireland most likely recognize "IST" as "Irish Standard Time", but people in other countries usually do not recognize what "IST" is. In CLDR, these zone abbreviations are managed as "short" names, and the coverage of short names is sparse in each locale. In this example, locale en-US does not have short name for Irish Standard Time. "IST" is used as the short name only in locale en-IE (IE = Ireland). Again, when a zone name is missing, CLDR suggests code implementators to use the fallback format.
CLDR is not cast in stone: CLDR called IST "Irish Summer Time" until CLDR 26 came out in 2014 - this fixed a bug with post-1968 timestamps at
the cost of introducing a bug for pre-1968 timestamps. I'm hoping that there is some way that we can fix this problem, a problem that exists regardless of whether negative DST offsets are used. Perhaps CLDR could be extended somehow, so that its reports the proper full names for time zones even if that info is not always deducible from the tzdb data proper.
So, the issue between Irish Summer Time and Irish Standard Time is irrelevant to CLDR with our current scope. -Yoshito