Extreme obesity

I stuff myself with a dozen dougnut ievery and what little weight I do gain goes to my ass

You might be bottom heavy. Unfortunately, where your fat goes depends on genetics. Just as you cannot spot reduce, you cannot spot gain.

I will say that if you gain enough weight, you'll get bigger all over.

Not sure where this idea comes from but you don't get to pick where the fat goes as you gain weight.
Most of my weight when I first decided to gain went to my thighs,butt and hips very little to the belly.
Actually it took me several years to see much in the belly so genetics has everything to do with it.
If you want to gain just make your portions larger at meal time.
My belly didn't appear until a few years later.
It was a high beach ball/beer belly and I wasn't real happy about that.
I lost a bunch of weight to have ankle surgery and when I regained the weight it all went to my belly but it wasn't a beer belly.
It was super squishy and flabby.
Thats the belly I wanted so badly.

Love your descriptive timeline on that belly of yours :-)

All of the fat that I gain goes right to my big belly.