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.
Which is only exacerbating the problem ... if CLDR is unable to support pre 1990 dates properly then we do need another service that can cope! Genealogical data and history in general can't simply be swept under the
carpet ... TZ while not promoting pre 1970 data does at least have it available. Now I know CLDR does not support historic material I can make
sure I avoid using it at all!
CLDR is able to support names used for pre 1990 dates only technically. If CLDR project really wants to handle the distinction between "Irish Summer Time" and "Irish Standard Time", it's doable. However, CLDR technical committee does not want to take an effort to localize zone names never used in last 30 years for hundreds of locales. It's just a policy issue. -Yoshito