What should I do if I have to apply for a Non-O retirement visa again due to early return home?

dont trudt anything you are told in immigrstion.double check independently .they dont make mistakes but they know how to f.k with your head .

You could you could have got a re-entry permit at the airport before you left it would have cost about 1000bht the you could of returned on your 90 day non O

Did you get a multi non I visa

If you can show that the money in your Thai bank account was transferred as an international transfer, then you can do it either way.

I would still recommend applying for the visa from your Thai embassy online again before going though. That's because it will save you at least 2 trips to immigration which can be harrowing affairs depending on where you live and which office you use.

If you apply online and enter with your non-O visa, then you can apply for the 1-year extension after you've been in Thailand for 45-60 days. You'll receive the extension the same day you apply in most cases, and be set for the next year.

If you wait to do it in Thailand, you'll need to go to the immigration office and apply to convert to a non-O visa. Then you'll receive an "under consideration" stamp and have to return after about a month to pickup the visa stamp in your passport. Then you'll need to wait 45-60 days and then go and apply for the 1-year extension. This means at least 3 trips to immigration, and 2 full applications at the office including letters from your Thai bank, bank statements, updated bank books, etc.

By doing it online, you save yourself a lot of trouble.

Yes, get your new Non-O before you travel