[tz] Issues with pre-1970 information in TZDB

[Guy Harris]

On Sep 22, 2021, at 4:43 PM, Tom Lane <tgl at sss.pgh.pa.us> wrote:

> Guy Harris <gharris at sonic.net> writes:
>> So does "best effort" mean "provide pre-1970 data in the default configuration if we have reason to believe it's accurate, but provide it only in backzone if we don't"?
> 
> That would be a fine policy in my opinion.  Indeed, up till the May
> changes I thought it *was* the policy.  Silly me.

I sent a message to the list noting that:

	stuff has been moved to backzone in the past;

	the backzone comment in 2021a speaks of at least some of the data there being questionable;

	as an example, America/Montreal, moved to backzone in 2015 or so, has comments suggesting it's not reliable, while Europe/Oslo's comment seems to suggests that the original sources agree with The Norwegian Meteorological Institute and thus that the data is presumably considered reliable.

Hopefully useful discussion of the "considered-to-be-reliable pre-1970 data vs. not-considered-to-be-relaible pre-1970 data" question will ensue.