When I refer to "magical redundancy", I'm talking about something similar
to an optional rule that appears in GURPS Martial Arts: Characters who
study more than one "style" can be required to learn the same skill each
time for a style. That is the "Karate" skill used in Okinawan Karate
would have to be learned separately from the "Karate" skill used in
Savate. (Note that in GURPS, the "Karate" skill really means "scientific
punching and kicking without anything fancy", not actually "Karate. Martial
Arts "styles" are skill clusters that include fancier moves.)
This is, of course, unrealistic in that it ignores the fact that there
will be some overlap, but it is meant to model the fact that there is
also some need for "re-learning" concepts and models when adopting
different overall approaches.
The masters then coalesce these into a syncretic style.