I read here: https://royalvacationdmc.com/blog/phuket-sandbox/
"Guests must stay at least 14 Nights in Phuket before traveling to any other Province around the Country. They will need to do an RT PCR test 72 hours prior to Departure. In addition, they must present it with the COVID 19 Vaccination certificate to the Checking Point at this Destination. "
Is this correct? I am thinking of someone who will do their 12 day test on 29 September, Night 14 is 1 October, so they will fly to Bangkok (if available by then) on 2 October. If they have their Day 12 test in the morning of 29th and fly to Bangkok in the afternoon of 2nd, they cannot rely on their 12 Day test to meet this requirement for a clear RT PCR test for onward travel as it is more than 72 hours
So in this example he should try to do his Day 12 test as late as possible so it falls within the 72 hour rule, or fly as early as possible on 2 October. Or do another RT PCR test.