In Bangkok, years back, they would send taxi drivers to do 90 day reports. It's my understanding that a representative, any representative, can do a 90 day
I don't know about Thailand but make sure you are stamped OUT.
I worked as a military contractor in the Middle East and Central Asia. We would fly in commercial and fly out military. Often we would have to look for somebody to stamp us OUT. In several cases someone would fly in to Doha, fly out USAF and when the tour was over fly USAF back to Doha. Well, they didn't stamp out and it's looked like a 5 month vida overstay. Big, big problem for them.
That used to be the case but it seems that it is no longer true. I was told time and time again over the last 5 years at Jomtien Immigration that if you remain at the same address - no big deal. I went to the US in May and went to Immigration just to check in late June. I was told the policy has changed but not fined. The next time, however, would be different. I think she said notify within 5 days but not 100% sure. Could be 3.
It is a good idea to have your re-entry permit before you go to the airport.
Not long ago I had to leave Thailand suddenly on business and did not have a re-entry permit on a new retirement visa. I was delayed in traffic and the desk was open but the attendant was not present. After a few anxious minutes someone showed up, took care of it and I did not miss my flight.