That's not logical to assume a master pickup builder can't scale down 1 model of pickup from 44 to 43 without it automatically making the parent pickup an arbitrarily chosen pickup built with 43.
The term “underwound” would assume that you have a pickup, then you take turns away from that pickup. Like with PAFs, the old trope is that it was overwound if they left the machine engaged too long while chatting with their neighbor, and underwound if they stopped it early for a coffee break.
So from a pickup maker’s perspective you wouldn’t refer to any coil that has a different wire gauge as an underwound or overwound version of it.
Like at 10k DCR the Screamin Demon isn’t an overwound PAF or Jazz coil, because those are 42AWG. The Demon is 43, which has been confirmed by other sources but also that answer is in plain sight. The Demon coils are skinny when compared to a Jazz. So a higher DCR + a smaller coil means smaller wire diameter. That’s basic physics.
So as we look at the Seymourizer, based on the size of the coils and the DCR, you’d probably notice it’s a little fatter than the Demon, and a little skinnier than the Custom. But if it were 44 like the JB/Distortion/Invader then it would be even skinnier than that.
I’ve always liked the idea of the Seymourizer/Distortion Neck as a moderate bridge pickup, with A5, rough cast, even A2. I did all that experimenting while I was at Duncan. My favorites for it are Alnico 4 & 6 actually.