Residents certificate from Immigration, A doctor's Certificate. You need to pass a test or two. Problem is you drive on the wrong side of the road. 🙂
It is clearly an issue that requires clarification. The post above is from Thai Legal's web site. I was made aware of this issue when I flew into BKK from Vietnam. Was not a major issue as I happy to fly back home and apply for an appropriate visa, But what was clear is that it is based on a calendar year and there was a limit in the number of entries, Makes sense that there are limits. Again this needs clarification