@Wayne ********
during the first year of the OA, each time you leave and re-enter you can get stamped with a one year permission to stay stamp. The OA visa expires at the end of the first year.
I entered Thailand with an OA visa in Feb 2017. I went to Cambodia in Nov 2017. I was given a 1 year permission to stay stamp when I returned to Thailand in Nov 2017. I got 1 year extensions of my OA visa starting with Nov 2018 and every Nov after that.
Extensions of the OA and O visas are the same except for the insurance requirement for the OA.
You can return to your home country to get a new OA and some people do that. You could also leave Thailand and start the process of getting an O visa again. Or you can just stay and get 1 year extensions of stay