When does the 90-day immigration notification period start after re-entering Thailand?

ah and the 90-day question: The 90-day clock starts at number 1 on the day you return. So your next report would be due on 30 of January (not Feb 2). You can do the 90-day report as soon as10 days before this date or even up to 7 day after this date and you should be ok

you could take the risk - it being late for reporting back anyways, and wait for your next 90-day report. You could also do your TM30 any time now, just pay the fine and be good. When visiting Immigration be prepared to pay a fine of around 800 -1600 THB for missing out TM30. And if you are living in a private home or privately in a rented accomodation, intend to stay or extend your stay, or are living on an extension already, it would be helpful that you show up with all documentation required to do a TM30. If you are living in a licensed guesthouse or hotel, you can ignore it, as they would have registered you already

did you do a TM30 any time before after arriving? As regarding the immigration Chumpon, myself I do not have any knowledge if they are strict on the handling or not

Dan Beattie the TM6 ist no proof of registration of an address, as you could as a foreigner write into it whatever came to your mind, without relevant proof or documentation, as at the point of entry, the immigration officers are NOT reassuring that the adress you wrote into the TM6 is correct. The TM6 is merely for Tourism of TH Ministry statistics purposes. Only the TM30 registration is regarded a valid registration. Some Immigration offices yet tend to waive it . . depends on where in TH you are living

I've never had to report my return. The entry stamp in my passport and the new TM6 is proof. The 90 days starts from the date of entry.