@Peter ******
just get a single re-entry permit for 1000 THB either at Immigration, or for 1200 THB at the BKK Suvarnabhumi Airport in "Departure 2" right before the exit Immigration desks, to keep the 90 days stay permit alive when you exit Thailand. The re-entry permit will be valid until December 23rd. . . . . . only when you get issued the 12-months extension, it might be worth considering if a 3800 THB multi entry permit fits the purpose. Because if you don't plan to exit and re-enter Thailand during these 12 months more often than 3 times, it saves money buying single re-entry permits prior to each exit