>Thanks. How often do these zip codes change?

Some zip code assignment change each year - either as a result of reassigning zip codes to split large zips up, or as a result of postal consolidation. Of the ~78K zip codes in use last uear, fewer than 50 were reassigned.

However, the mapping of Zip Codes to city names shifts frequently - you may have the same zip code refer to multiple cities/towns, and these change due to redistricting and changes intown incorproations.