I just did a simple test.
I have removed randomly 3 styles from MIDI set #61.
Rebuilded the style data base.
Restarted BIAB and checked what addon's do I have : 'You have all of the Style disks (unless we've made some new ones) have all'.
Status : the 3 missing styles are not detected.
Yes, everyone's answers are very worthwhile and very much appreciated, but I think this is the actual issue.
The program itself
does not correctly calculate what is there and what is missing.
I think I need to report this as a problem.
In the meantime, I'm off to Excel.
Trev