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

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.