In my early days here in concert hall any other software except Hauptwerk was unwanted. Now CH is open to other software (GreatOrgan, JOrgan, Hauptwerk IV, Hauptwerk V, Organteq & Pianoteq) but GrandOrgue is not selectable.
The GrandOrgue code base grew out of MyOrgan, which was a clone of Hauptwerk v1. The programmer of MyOrgan eventually admitted that his software was a clone, and gave his code and copyright to Milan Digital Audio, but by that time he had already released the code as opensource. The further development under the GrandOrgue name has included MDA in the copyright notice, and the programmers have worked on phasing out the code from MyOrgan with new code and functionality. The Hauptwerk forum effectively banned any posting of GrandOrgue related content as any unencrypted Hauptwerk sample set can be made into a GrandOrgue set.
That’s probably why it’s not listed here.
I, personally, have been involved with jOrgan, GrandOrgue, Hauptwerk, Grand Organ, Miditzer, and other sample and modeling based software organs. I’d vote for it to be included in the list, but it’s obviously not up to me :)