I am not able to shed a lot of light on the matter of keys raised by
Gene Kuntz (Hi there, Gene! - Well done!), only to say it is a curious
anomaly where MIDI organs are concerned, and I understand the problem.

My own organ, "King Solomon", plays on 5 MIDI channels simultaneously
and can play all the following list of notes individually: 12 Bass,
7 Accompaniment, 32 Melody, 32 countermelody including glockenspiel,
24 trumpets, 24 Octave-forte, 12 percussions, a 49-note accordion and
6 registers; a total of 198 active MIDI outputs.  It would take an organ
book 198 notes wide to emulate this degree of control.  To describe it
as a 198-key organ sounds a bit fatuous, but that is what it is the
equivalent of.

If people ask, and they do, I call it a 162-key equivalent organ
(a figure I just conjured up).  Perhaps someone, somewhere, has the
appropriate answer.

Bob Essex