@Don *****
Hopefully, you are correct. But correct me if I am wrong. It is the Thai government and individual tax offices capable of misinterpreting and modifying tax regulations which will be the final arbiter of what actually unfolds, and not the SSA in the USA. Just as the embassies, consulates, and individual immigration offices routinely interpret, misinterpret, change, modify, or make regulations and requirements more stringent regarding visa categories and extensions, nothing is stopping several hundred individual tax offices from doing the same. You are correct, though.
Currently there is not a box on the Thai Income Tax Form for nonassessable income.