Question on id stability

[Mark Davis]

I have a couple of questions that I hope someone can give guidance on. These
are sparked by the change from IDs like "America/Catamarca" to
"America/Argentina/Catamarca"

In CLDR (http://unicode.org/cldr/), we are using the IDs to access different
localized names for the time zones. Each time a zone ID changes, we have the
choice of either updating all the localized files that use that ID, or
leaving them be and using the old ID. To make our maintenance easier (and
make it easier for implementations), I'm inclined to recommend that we
maintain stability as of a given date; that we never change an ID after that
point.

1. Would there be any downside to such a policy?

2. I was not able to find documentation as to whether there is a policy
disallowing 'retired' IDs to be reused later for a different timezone. Some
might think that it is so obviously a bad policy to reuse IDs that it
doesn't need stating, but ISO has reused country codes, for example, causing
no end of problems for stability.

3. What was the reason for the change for Argentina? Is this a one-off
aberration, or can we expect America/Chicago to change to America/United
States/Chicago, America/Vancouver to change to America/Canada/Vancouver, and
so on down the line?

4. Are links expected to be definitional and stable? That is, if I ever have
two IDs that are related by a link:

Link A B

Can it ever be the case in the future that the IDs A and B are "unlinked",
and given different rules? Or is it that links in certain files are stable?

5. A side note: when examining the links, and assuming that they are of the
form

Link <new> <old>

there are a small number of links that are "not final", meaning that what
they link to, itself links to something else. While not formally an issue,
it might be more convenient (and transparent) if these were put in a
'canonical' form.

13 America/Rosario => America/Cordoba # NOT FINAL =>
America/Argentina/Cordoba
39 Brazil/Acre => America/Porto_Acre # NOT FINAL => America/Rio_Branco
79 GMT+0 => Etc/GMT+0 # NOT FINAL => Etc/GMT
80 GMT-0 => Etc/GMT-0 # NOT FINAL => Etc/GMT
81 GMT0 => Etc/GMT0 # NOT FINAL => Etc/GMT
82 Greenwich => Etc/Greenwich # NOT FINAL => Etc/GMT
99 Navajo => America/Shiprock # NOT FINAL => America/Denver
137 Universal => Etc/Universal # NOT FINAL => Etc/UTC
139 Zulu => Etc/Zulu # NOT FINAL => Etc/UTC

‎Mark