PG embed chords in a part of the the midi file, but these can only be read in BB/RB/PT.
But the BB Chord Output track are just held chords that are easy to read/detect, it is not trying to detect the chords in a midi song with lot of tracks, just one track with held chords. There is a style with held chords PNOSIMP4.STY but it plays inversions so it don't read them correctly.