Do multiple entries on a type OA multi-entry retirement visa each grant an additional 12-month stay in Thailand?

David Bonar, and a 1 year multi-entry VISA means it's GOOD for one year ;)

Be that as it may I hope I have straightened out your misunderstanding on how the visa works. :)

Believe me you're far from the first person who mistakenly thought that about that visa.

David Bonar Nope, you missed a critical thing about that O-A visa.

It's good for a YEAR from the date it's issued, every entry DURING THAT YEAR gets you stamped in for another year.

Meaning IF you exited/re-entered the country just prior to the VISA expiring you'd get stamped in for a whole new year

As soon as the visa expires so does the ability to get a year stamp.

All you can get is about 2 years of stay from that visa