A Non O-A visa is a multi entry visa that is valid for one year from date of issue.
During it's validity, every time you enter Thailand you are stamped in for 12 months.
So ...if you exit and reenter just prior to expiry you receive another 12 month stamp.
Hence you can obtain 2 years stay out of the visa.
After which you would either obtain a new Non O-A OR start obtaining extensions.
Note: Insurance required.
A Non O retirement is a single entry Visa. When you enter Thailand the visa is "used" and you are given a 90 day stamp.
In the last 30 days of that stamp you apply for 12 months extension.
This has financial requirements.
Note: Insurance not required.
For extensions from a Non O-A and a Non O (retirement) the financials are exactly the same however the extensions from the Non O-A require insurance.
Guys with a Non O-A and able to base their extension on marriage then Insurance is not required.
Note: The very first extension from a Non O-A would have to be based on retirement.
Note non O-A can only be obtained in own country or country where you have resident status.
Non O retirement can be obtained at most places outside of Thailand.
Previously at consulate/embassies and now using eVisa.
The Non O-A previously was a ripper Visa when it had no insurance requirement.
Especially for those that returned home every couple of years and also did not wish to have funds sitting in a Thai bank.
Not surprising that many folk with a Non O-A stamp and needing extensions based on retirement decided to exit Thailand at some point without reentry permit to Kill Off the Non O-A.
Reenter Thailand and obtain a Non O retirement reason being no insurance requirement.
Note: Also Non O-A application has some requirements that Non O does not such as Criminal background report, medical, etc.
Outlined here.
https://www.mfa.go.th/en/page/non-immigrant-visa-o-a?menu=5e1ff71bc4281a00c812e8e2