that is sometimes a problem at airports. The checkin people are not always up to date with the rules.Maybe almost impossible, get travellers to all over the world. I have had same kind of problems but asking fotr the supervisor is sometimes the easiest way\ to solve the problem.
yes but question was about flying to the usa and your reply was about returning to thailand. My answer was on returning to thailand too. No special extra costs exept the well know costs for entering thailand.
why? Flying to thailand is a new start. Coe etc etc nobody cares how you flew to the US. Do not even have to mention it if you decide to apply for flying to Thailand