Simon, is the chord hierarchy documented in a file accessible to users? If not, should it be? If so what is the best search term and location to hunt for it?
I believe it's part of the "secret sauce". I'm also pretty sure it's done on a case-by-case basis depending on the RealTrack in question.
While you are at it
.. what are the colonel's secret spices?

I'll give you a hint - the first one is:
This to me clearly implies that BIAB handles sus2, add2, and add9 chords the same as a 2 chord. All four chord types give you the same thing. PG Music, is that wrong?
I've personally seen some RealTracks that have both sus2 and add2 chords in them. These would be some of the newer "12 key" RT's - don't ask me which ones though, I don't remember.