[jitl]

A timezone changing or being eliminated doesn’t erase the history of that timezone. So you can still use the last definition of such a timezone if the date is still in the future, or use the appropriate definition of the timezone at the time of a date marked in the past.

[williamdclt]

> you can still use the last definition of such a timezone if the date is still in the future

but that'll possibly give you an incorrect time!

If you want to store "8am in Paris on the 2026-01-01", then you store "2026-01-01T08:00:00 Europe/Paris". Great, if Paris decides to change their offset rules, that's fine.

Currently, that would be `2026-01-01T08:00:00+01:00` but if Paris decide to ditch DST, it could become `2026-01-01T08:00:00+00:00`. All good, you stored a timezone rather than an offset, so you're decoupled from the timezone->offset changes.

But if tomorrow `Europe/Paris` cease to exist, and is replaced with Europe/NewNewYork? The last definition of Europe/Paris would make this date `2026-01-01T08:00:00+01:00`, but if Europe/NewNewYork ditched DST then it wouldn't be 8am for the people living there, it'd be 7am.

You're decoupled from the timezone->offset changes, but not from location->timezone changes.

[jitl]

The reason the zones use city names is because city identity is far more stable than national or regional borders. Still, the system can gracefully handle deprecation of a zone name. If Paris is renamed NewNewYork by edict of some new global despot, the IANA will just alias the two names together.

See https://github.com/eggert/tz/blob/main/backward for all the deprecated zones.