Firstly thank you for all the useful advice on this page, I know you guys work hard for nothing :) Secondly, does anyone know how long a re-entry permit is valid for? Our next extension of stay is due in July (non-B) and we're wondering if we get a multi re-entry now if it will still be valid after the next extension. Thanks for any help :)
TLDR : Answer Summary
The validity of a re-entry permit in Thailand lasts until the last day of the permitted stay as stamped in the passport. If you extend your stay under a NON-B visa, you will need to apply for a new re-entry permit to maintain travel permissions after the extension.