Sonora going to year-round standard time; Atyrau switched zones twice?

[Paul Eggert]

A while ago Gwillim Law sent me a summary of the time zone changes in
the 1999-09 IATA Standard Schedules Information Manual, and I finally
got around to looking at them.  Here are changes that are not in the
current tz tables:

   Mexico:  The state of Sonora is going on year-round Mountain Standard Time.

   Kazakstan: Atyrau switched from Western (Kazazhstan) time to
   Central in mid-1997, and switched back in mid-1999.

Does anyone on this list have more information about these changes, in
particular, details about exactly when the changes occurred?  I tried
to confirm them on the web, but my Spanish is limited and my Kazazh
nonexistent.