There is one point of importance missing from this discussion, the "way of teaching" a M.A. is an inherent part of that M.A.
Note the Shodokan split from Aikikai, once the methodology has a significant change, the art itself changes.
I would expect this to be even more evident for Koryu.
Shodokan Aikido is a good example, but really Ki Aikido, Yoshinkan Aikido, Iwama Ryu - they are all separate because of a teaching methodology.