I'm not talking about the forms now... He could have mastered one form at most just learned about the others, but I don't even think he mastered one form.
I think he started learning one and then strayed from that and started developing his own form from that. He had the knowledge the experience and Tulak his holocron to base it on. Seems like something he would do (there is no real evidence from this besides the movie where Revan is captured).
I was talking more about the force techniques. But he could have probably mastered at least one form in those years, if he did follow one form. Reason I believe is so because he did fight for years and usually when you are fighting you increase your fighting skills faster.