As I understand it, that is what you would have had in tz 2021a, but not in the just-released 2021b (unless you enable backzone, but if some distributors start doing that then it's effectively a fork).
I think the API promise is that even if there are known discrepancies pre-1970, the standard database already might not be including that, and so people with pre-1970 timestamps already should have been using backzone.
