[tz] Issues with pre-1970 information in TZDB

[Guy Harris]

On Sep 23, 2021, at 10:31 AM, Tom Lane via tz <tz at iana.org> wrote:

> That's fine, but if that is the policy, then the data should in fact be
> valid (to the best of our ability) for the named location.  It's not okay
> to present data for Europe/Oslo that is simply known incorrect for Oslo.
> Whether it's exact for anywhere else in Norway is a red herring.

So what is a given tzid supposed to refer to when using it for pre-1970 data?  The city in its name, and no other location on Earth?

If so, that puts further restrictions on the use of tzdb for pre-1970 dates and times, over and above "this data is based on whatever sources were most recently used to produce it; the correctness of that data depends on the sources used, and some sources are known to have made a number of mistakes, and that data is also subject to change as if more demonstrably correct data is found".

(It's not acceptable to say "the city in its name, and no other location on Earth" for post-1970 data unless everybody's willing to have an *very large* number of tzids, maintain such a tzdb, and use such a tzdb.)