I see two possible problems with using references to an authority
that changes over time:
- Tags used in old data may be left without a resolution mechanism
(such as when a language or country disappears or is renamed).
This may be solved by keeping a registry of old names around, and
should not be a terrible problem.
- Tags used in old data may be turned into valid names for something
new because of the reassignment of the name. This is a real problem,
but I think the registry agencies are fairly aware of this.
The changes made so far seem to be corrections.
The problem that the real world changes is not going to go away soon.
ISO has been fairly consistent in the past about not handing out
new country codes that reuse an old allocation. Other problems
(like Moscow Russian now being ru-RU rather than ru-SU after the breakup
of the Soviet Union) we have to live with.
The references to ISO 639 are intentionally equipped with dates, and
the registry maintainers are listed, exactly to make people aware that
these things change over time.
I don't think we should do anyting different; second-guessing ISO is not
something the IETF should be doing, IMHO.
Thanks for the praise!