[tz] Some thoughts about the way forward

[Guy Harris]

On Sep 23, 2021, at 10:25 PM, TJ via tz <tz at iana.org> wrote:

> As a user that will be affected by this, I am more concerned by the
> practical aspects. I make extensive use of the tzdata between 1900-1970
> and have data that depends on the stability of the offset calculation
> from the timezone stored in the form of America/Los_Angeles, etc.
> 
> I have never used the backzone file, so I do not want to import
> extensive amounts of extraneous zones, but I would like to keep the
> newest changes post-1970.

"I have never used the backzone file" means that you are currently getting Toronto rules for America/Montreal, so presumably that's OK.

And presumably you have only been using that data since 2015-04-11 or so, otherwise you *didn't* have stability for the duration of whatever use you have - prior to the 2015c release, America/Montreal was in the northamerica file rather than in the backzone file.

(America/Montreal is not the only item that moved from the main files to backzone in the past, so "America/Montreal isn't a problem" doesn't necessarily mean that there are no problems.)

Note also that if you want stability of the offset calculation, and somebody else wants errors in pre-1970 timezone information (which may well be present in that information), one of you will have to lose.