These label names are sourced from a handful of different places:
fullsnes, for the IO registers $00F0-$00FF of course
This copy of eb_spc.txt, which has a few label names for sound effects contributed by Catador and way too many comments by me
kokichi.c -- a while ago I started trying to write high-level code, as I was working my way through eb_spc adding comments about the control flow. I didn't get very far. A few of the variables were written out in fuller words than in eb_spc, though.
A few labels from those disassemblies may be sourced from the sneslab wiki, which has descriptions for variables in a completely stock version of N-SPC.
These label names are sourced from a handful of different places:
Not all of the names were carried over (yet).