As pointed out in another post, the way timezone rule changes are stored actually does effectively what you are saying. For each time zone / locale, when there

As pointed out in another post, the way timezone rule changes are stored actually does effectively what you are saying. For each time zone / locale, when there is a rule change, it is appended to the existing rules along with the date of the change. Example from the tzdata2015b file for the New_York time zone: # Zone NAME GMTOFF RULES FORMAT [UNTIL] Zone America/New_York -4:56:02 - LMT 1883 Nov 18 12:03:58 -5:00 US E%sT 1920 -5:00 NYC E%sT 1942 -5:00 US E%sT 1946 -5:00 NYC E%sT 1967 -5:00 US E%sT