I never paid too close attention to the pressed coin machines during my visits to TDL. So I'm assuming that the coins with the months on them came from machines that had their "plates" changed monthly? That's incredible! I don't think we'd ever see that here in the U.S. parks.
That's a good question Tokyo. Not sure. They might have been changed the plates monthly, or maybe they offered the 12 months all of the time.