The airline at your departure destination is who would ask you. We booth throw away train ticks for $12 each our last trip because we didn’t know when we were leaving. Check with your airline to see if train travel is acceptable. If you do get asked you will have to buy a return ticket to board and that can be very expensive. You could gamble and probably won’t be asked, buy you just never know.
I think the point is, you may make it in 100 times, then the next time you get asked. Like you, I have come into Thailand many times without issue. It’s always a gamble!