Tzdata intends to be accurate since 1970, but Windows has fewer timezones so it couldn't possibly be as accurate. There is also a historical extension to tzdata somewhere. (Tzdata, used by Unix, has a model that asks what timezone offset rules this place uses at some time, and collates timezones based on common answers: whereas Windows models change by saying that some place switched from one pre-existing timezone to another and only asks what timezone offset rules this place uses now.)