I did copy the Artist Tag to the Album Artist last night on all the files after I 1st posted this (I mentioned this earlier, before I changed,it was blank). That would be the only thing I've changed.
The tags that belong with one of the tracks on a compilation album do have both sort artist (soaa) and sort album artist (soar) tags set as VA. Some - but not all - also have that itunes comp, and a pgap (whatever that is)
There's a whole lot of files, so I don't have time to check them all, but from the few I have looked at, only the tracks that are from compilation albums and have VA as Album Artist are getting the embedded sort tag, which I guess is why MB assigns it globally
I've just started digging into the new sorting options, so I haven't figured out what's what yet, and probably have been doing a lousy job explaining what I have (or haven't) done