When I was in Iran they changed the calendar three times. First the Shah changed the year by adding 500 or so years so that the calendar started with the founding of the Persian Empire by Cyrus the Great. This didn't have the unifying effect that he had hoped for and just caused a lot of ill feeling and confusion. So he promptly changed back to the western calendar. When the Ayatolla got into power he changed the calendar to the Islamic one.

All this happened in the space of less than a year. Guinness book of records, where were you?