Thomas Munro <thomas.munro@gmail.com> writes:
> As for whether it's valid, that's coming from the IANA tz dataset. It
> has a moment that it believes standard time to have begun at each
> location, in this case:
> Z America/Mexico_City -6:36:36 - LMT 1922 Ja 1 0:23:24
> https://en.wikipedia.org/wiki/Time_in_Mexico#History seems to agree on
> the year at least. That "local mean time" offset is computed from the
> location's longitude, for lack of anything better. The tzinfo
> "Theory" file has a bunch of disclaimers about pre-1970 data though,
> including "the tz database's LMT offsets should not be considered
> meaningful".
I tried to interest them in dropping the LMT idea altogether [1].
Unsurprisingly, the proposal went nowhere.
regards, tom lane
[1] http://mm.icann.org/pipermail/tz/2021-May/030114.html