Seems like a silly question.
I noticed some of the Arcade Cores have a new "CRT" Adjust option for Vertical. +8 to -8, and although they work great I'm partially convinced the change is permanent to the CRT.
I used one Core in Arcades (don't remember which one) and, after adjusting the Vertical upwards, whenever I power on my Sony XBR CRT, my geometry has gone up so there's a black void at the bottom. I'll try seeing if readjusting the Vertical adjust brings it back to normal, but just found this unusual and not sure if it was intended to be a permanent adjustment.