I have just re-entered thailand on my multiple entry O-A visa. It is valid until Dec 13. I left Thailand for a few months and just arrived back today. They stamped it as valid until December 13. Should it not have been good until October of 2023? My required health insurance will expire around the December date. Will I be able to have it stamped valid until October of 2023 once I have renewed my health insurance?

When you enter Thailand on a valid Non-OA visa you receive permission to stay equal to the expiration of your mandatory health insurance or one year, whichever date comes first.

It seems you were stamped in according to this rule.

Thirty days before your current permission to stay (or forty-five days before at some offices) you would be able to apply for another extension of stay.  When approved you would receive additional permission to stay equal to the expiration of your mandatory health insurance or one year, whichever date comes first.  Merely, renewing your health insurance would not cause your existing permission of stay to increase, but would have to be done in conjunction with a new application for an extension of stay.

Once you get your insurance sorted you could leave and enter again to get the year without having to pay for an extension.  You have to do this before your original visa expires.

 

At this point though it is probably cheaper just to pay for an in country extension.

 

You need to get your insurance and visa/extension expirations dates aligned.  For an O-A they will only extend you to the expiration date of the insurance if it is less than a year.  I lost 1 day last year because for some reason Pacific Cross changed my expiration date by 1 day when I renewed.

I came back into BKK two weeks ago.  My current OA Visa Health Insurance expertise on Jan 14 2023. Therefore i got stamped in until Jan 14, 2023.  I plan on getting the insurance policy renewed in December 2023 until Jan 14 2024.  I also plan a one day trip to Kuala Lumpur in late December and I should be able to get stamped in until Jan 2024(at least I hope so but with TIT??).  In the end this is the plan.