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

[Robert Elz]

    Date:        Tue, 28 Sep 2021 16:38:30 -0700
    From:        Paul Eggert via tz <tz at iana.org>
    Message-ID:  <086e075f-05fc-4f4f-a2ff-c4eeb2f2ab2f at cs.ucla.edu>

  | Also, the 'backzone' line you're referring to ("-1:00 - -01 1960 Jun 20" 
  | [1]) is surely wrong,

Do you have some evidence for that?   Are you claiming that (what is now)
Mali used something other than -1:00 from 1934 to 1960?   Or just that the
precise date/time of the change "cannot" be correct?

If it is the latter, then without evidence of the change happening at
some other time, I would tend to believe that as it is written.   Independence
had been agreed with France months earlier - that is, they had plenty of
time to prepare, and was to happen (and happened) on that date.  Assuming
that part of the preparation was to switch timezones along with independence,
which is not an absurd suggestion, then that rule seems entirely plausible
to me.

  | and so doesn't belong in a high-quality 
  | timekeeping database regardless of when Mali became independent.

And you believe that a high-quality timekeeping database when converting
times from (what is now) Mali in 1950 should produce answers that are an
hour incorrect?

If the answer to that is "it is before 1970, so we promise nothing" then
that same answer would also apply to the earlier rule, as it was, even if 
wrong, but then while there might have been a few hours, or even days or
weeks perhaps, when the answer was wrong, surely that's better than 26
years of erroneous answers?

  | The more we get bogged down with irrelevant 'backzone' trivia like the 
  | date of Mali's independence,

There's no need to get bogged down with that, I don't believe that is
disputed.   In cases where independence came via revolution, then the
exact time it happened could be disputed.   Not here.

And who or what has been bogging us down with that discussion?

I've just done a search of my copy of this list, and the only mentions of
Mali that appear at all, are in Michael H Deckers recent message, and then
your reply (and then there will be this message as well, eventually - maybe
some more recent messages in the past hour or two or following this), and
locations where Mali has appeared in tzdata in a patch (either as its
data was being amended somehow, or when some other nearby data was and
it was caught in the context diff).   (My copy of list data goes back to May
1988...)

  | the less time we'll have to make genuinely useful improvements to tzdb,
  | such as some of the improvements recently discussed on this list.

I must have missed something, but there have been lots of recent messages,
so that is possible but I have no idea what improvements you mean.

Some data corrections, sure, and many of those pre 1970, and while those
are likely improvements, I cannot see how they're any more important.

Aside from those, I don't recall anything recent that is really any kind of
notable improvement.

  | Let's focus on these improvements rather than rehashing past mistakes.

One improvement needed is to fix the past mistakes - like that one.
"We got it wrong, sigh, never mind, what's next" isn't a good approach.

kre

ps: why does Pacific/Honolulu still exist as a zone given the apparent
policy?   As best I can tell it is identical to Etc/GMT+10 for all dates
after 1970, so shouldn't it also be moved to backzone and made into a link?
Further a comment just above its rules says:

# We're left to guess the time of day when Act 163 was approved; guess noon.

and the rule incorporates that guess.   That's far less likely to be
correct than that Mali's timezone changed at midnight on the day of
independence.

But no, I am not suggesting that actually happen - far from it - but if
the requirement for fairness was to eliminate everything that isn't needed
for post 1970 accuracy, then surely that is required.   Of course I don't
think I'd like to be a TZ coordinator in the US if the US press discovered
a plan to wipe Hawaii off the map.