I recently moved from Pattaya to Sa Kaeow province and when I did my 90 day report immigration said next time I would have to apply for the annual extension with the full "here's one of me and the wife at the front of the house" supporting doc. My current externsion will not have expired by then. I thought subsequent annual extensions only required bank statement? Is this usual on changing province?

For marriage always requires wife and full documentation. As you have moved they need new photo group from current residence.

This is why I say that it is easier to keep a retireent visa if you have one. Less hassle than a marriage visa.