Thailand has a very complex visa system and sometimes it seems like it's forever changing.
My advice to anyone who has an important visa-related question is to go to your local immigration office or Thai embassy and get the answer from the people who make the rules.
Don't rely on info from well-meaning 'experts' (including me) who think they know the ropes. Their info might be correct at the time of writing but they could also be wrong.
For that reason the answers to the questions in this section should never be taken as absolute gospel.
The level of customer service at Thai immigration offices has improved a great deal over the past years and I always find them very helpful. Even in the smallest provincial immigration offices there will invariably be an officer who can speak enough English to help you.