[tz] Merged 1970+ time zones should always return -1 pre-1970

[Derick Rethans]

On Tue, 28 Sep 2021, Paul Eggert via tz wrote:

> On 9/28/21 11:59, Michael H Deckers wrote:
> > > America/New_York, for example, merges many regions that did not observe
> > > the same time before 1970. 
> > 
> >      Yes, but it merged only zones that _never_ had an entry in tzdb.
> >      What we are doing now is merging tome zones that have existed
> >      separately for years within tzdb.
> 
> 
> There are many examples of those merges too. For example, Europe/Zurich
> currently covers Liechtenstein even though before 2013 there was a separate
> Zone for Europe/Vaduz.

And IMO, there should be a seperate one for Europe/Vaduz if any data is 
different.

> And anyway, saying "we've always done it that way" would not be an 
> adequate response to valid fairness concerns.

"Fairness" is also not "because we don't have accurate enough pre-1970 
data for one region, no other region can have this data either". Which 
is what you were doing with the Oslo/Stockholm/Berlin and 
Brussels/Amsterdam merges.

Fairness would be to allow pre-1970 mostly accurate data to available 
for *all* (ISO) regions.

I understand that for some use cases, people might want the smallest 
possible binary size. Make a switch for *that* use case instead, with 
the default being what we already had pre 2021b, or potentially even 
undoing some of the other destructive changes that have been brought in 
since you took over as TZ Coordinator.

cheers,
Derick