[tz] Issues with pre-1970 information in TZDB

Guy Harris gharris at sonic.net
Thu Sep 23 21:38:16 UTC 2021

On Sep 23, 2021, at 1:12 PM, Tom Lane <tgl at sss.pgh.pa.us> wrote:

> Guy Harris <gharris at sonic.net> writes:
>> 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?
> Why not?  That would seem to be the obvious interpretation.  Besides
> which, the existing practice of citing LMT for pre-standardization
> dates already limits any arguable exactitude to the city's meridian.

OK, then let's make that explicit in, for example, Theory, by indicating that if you use the pre-1970 data for a given tzdb region for anything other than the city that appears in the tzid, there is even less guarantee of correctness than if you use it for the city.

What if that data 1) has been determined to be correct based on sources we deem sufficiently reliable and 2) it applies to more than just the city and its environs, but it doesn't apply to, for example, the entire country?  Should one or more new tzdb regions be created for those other locations?

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