Is there an 'under consideration' period for a Non-O visa extension based on marriage in Thailand?

I think what you're confusing

@Hen***

is the fact that you are doing two completely different things with different departments inside the immigration office.

You applied for a 90 day non-O visa based on marriage, met the requirements to do that, most likely had the home visit to get that visa AND it went under consideration the 14 days before you went back to get the Non-O visa and new 90 day stamp inked into your passport.

Now you're applying for a yearly extension of stay, you'll meet the requirements to do that, get a 30 day under consideration stamp and during that time most likely have an in home visit to get the extension and then at the end of the 30 days you go back and get the year extension inked into your passport.

It's two separate things that require two different vetting processes. Believe me they're not singling you out by any means.