There are a great many martial artists who claim to have studied more than one system, and this is never a real problem. Any intelligent martial artists is going to study one core system, and then fill the holes in their self defense through cross training in whatever system they feel best addresses the shortcomings of their core system.
But there are those martial artists who claim master rank in two or three or even more styles. This is impossible.
For you to legitimately be considered a master of a system, I would think it necessary to be a true in your heart follower of the core beliefs of that system. If I believe that Hung Gar is the ultimate martial arts system (which I do) I could not also think that taekwondo is the ultimate martial arts system. The core beliefs are completely different. Hung Gar sinks energy and roots into a solid “immovable” stance. Taekwondo takes to the air with a kicking assault. The philosophies cannot co-exist.
Now, there may be those who are quick to point out that I teach both systems, and they would be undeniably correct.
But – I do not claim mastery of both systems.
There are many masters who make claims of such mastery. There is a guy in my area claims to have combined such diverse arts as Taiji and Muay Thai.
It can’t be done. The most basic fundamentals behind the basics of these two arts are polar opposites! It simply cannot be done.