Tafia

I also have non-immigrant O-A (retirement) with multi-entry. I am due to extend this Friday. Although this is my 2nd extension I still can't remember the title of all the documents needed. Last year I filled all out at Udonthani immigration instead of on computer. I do know that I have to have income statement (have), passport (obviously) w/pictures and of course baht. Last year I had to have "landlord" blue book copy, this year the wife has blue book for our (her) house so I'm guessing copy of it along with her ID, show bank book (they weren't interested in the money in it, just that I had one), and draw a map from house to immigration. To be clear, this is NOT a visa based on marriage. What I don't remember are the forms to be filled out for the extension and multi-entry (TM 8?). Can anybody post the forms (just the TM/title number I would think) needed, I think the same would apply to the OP. It is also pretty clear that the requirements of the local immigration office may change from year to year or day to day, although I will say that so far working with the Udonthani Immigration has been quite pleasant.

As a note, going in and out of the country will reset your 90 day report, but not expiration of O-A visa, as I understand it. At least that is the way it has worked here in Udon. While the multi-entry is a bit expensive initially, it sure beats all the paperwork every time you wish to leave and return and one can do so at will without a hassle.

Thanks

"If you are back in Thailand before the 28th Sept (before visa expires) you will get stamped in for another 365 days"

Before the actual visa expires is correct.  
I'm not so sure that date is 28 September.