Learning it and mastering it is two different things.
Learn it: Be able to do it with relative ease
Master it: Mix it up with other moves
You're mastering it if you're able to Jump Cancel easily
with other moves individually as well as being able to do it consistently with other moves. You aren't mastering JCing if you're doing it with one move. And switching in between weapons merely tests your timing in different situations. You're still learning how to JC when you mix it with different moves since you're relearning the different timings between weapon switching as well. The only way you know that you have mastered it is that if you are able to do it fairly consistently without messing up frequently.
If a person learns to JC Yamato Rave multiple times in succession, they are just learning how to JC one move. It is still considered to be learning how to JC but you aren't learning how to integrate it in your gameplay while using other moves. But if a person learns how to JC Yamato Rave, followed up by Lucifer and Pandora, they are learning how to JC more effectively because they are using different moves.
In the video above, I teach players how to integrate Jump Cancelling with multiple moves at a fairly slow pace in DMC4. Even if someone manages to master the combo that I taught them in the video (skip to 8:30) they aren't learning other elements of JCing with other moves that they haven't attempted to learn.
