Can I use a multiple re-entry permit for my Non-O visa after getting an extension in Thailand?

The date of my Non-O based on retirement was not the date of application or date I picked it up. It was a date 10 days after the application. It was probably the date they processed or approved it. This was in Chiang Mai.

okay, let's take a breath and take a step back 😕

you haven't even gotten the Non-O visa and new 90 day entry stamp inked in yet.

How about you wait until you do that and see what the expiration date will be on it and then work the clock backward to see when 45 days or less is ?

As far as a re-entry permit, it works like this;

IF you buy one right after you get the Non-O visa and new 90 day stamp it's good ONLY for the time that stamp is good for (so 90 days)

You have to wait until you get the year extension inked in and THEN buy a re-entry permit <- that one will be valid for the whole year the extension is good for.

So if you're going to exit/re-enter the country during the 90 days that you'll get when you go back on the 12th get a single re-entry permit (1000baht)

and

after you get your year extension you can get a multiple re-entry permit (3800baht) which will be good the whole year