OK, we are now back in Thailand! Let me recap...
Saturday - Took Pre-flight PCR test in Singapore prior to Monday's flight to BKK
Monday - Received POSITIVE result! Apparently from residue antigens of Covid from early February. No symptons. Canceled flight booking.
Tuesday - We could get Singapore Certificate of Recovery after 7 days and leave Friday. But then would have to apply for a new ThaiPass ????. So we got antigen test from Dr. Ti ((DTAP clinic, highly recommended)).
Wednesday - Got antigen results and the Letter of Recovery from him based on the low antigen count, stating that Covid was 6 weeks old and not infectious. Changed SHA+ hotel booking and made flight booking for Thursday. Within 72 hour ThaiPass flexibility limit.
Thursday - proceeded to Changi with CoR not up to Thai standards (should show positive Covid test more than 14 days prior), but why not? We were told by Scoot at Changi that we could have boarded plane on Monday with Positive result (??). Anyhow, were not impressed with my Singaporean CoR, and asked if we had anything from February showing we had Covid. Not really, we said. How about a picture, they replied. For some reason I had a picture of two positive ATK tests dated February on my phone - that got us on the plane! little problem with the 72 hour out of date ThaiPass in Bangkok, but not much. BKK Health inspector happy with Singapore CoR, did not look at ATK pic. Hotel took PCR sample upon arrival.
Friday - PCR test comes back Negative! <deleted>! We are free to go.
Things are changing fast, but my one regret was not going to the airport on Monday with the Positive result and see what happens. Also, if you have had Covid - get a Certificate of Recovery.
All good now, already had some Phad See Ew to celebrate. Hope this is useful to somebody....