I think it really depends on what you mean with "mastering" one style. If your goal is to master the entire parts of a style (Stage version, folkloric version, folk dances, different styles of the stage version, different time periods etc.), then it is impossible to master more than one style. But if your goal is to master parts of a style (let's say stage version of a certain period and folkloric version of some areas as well as 1-2 folks dances), then IMO it is possible to master more than one style. Me for example surely can dance the classical modern Egyptian Raqs Sharqi (this means the style of the early 70ies to the early 90ies) quite well, as well as the folkloric stuff which belongs to a Egyptian routine of that period (Raqs el Assaya, Baladi, Raqs el Sagat -zills-), but I am not a big expert on Khaleegy (which has become very popular in the modern Egyptian routine since the middle of the 90ies) and I definitely don't dance the modern Cairo Raqs Sharqi (well, actually the differences between those styles are rather subtle, but nevertheless....). I also don't dance Egyptian folk dances, but do I have to? There are no possibilities to perform them anyway, except maybe very rarely at a stage show. But since I mainly get hired to perform Raqs Sharqi, this is what I have concentrated on. On the other hand, I am surely an expert on Greek Tsifteteli, because I've been brought up with it. And I'm not talking here about my own Greek-Arabian fusion, which I call "Tsifteteli Oriental", but I'm talking about the traditional Asia Minor style Greek Tsifteteli, which I learned from my grandparents who came from there. And then, I dance and teach also some fantasy and fusion stuff, like for example veil dance (plus that I can dance also the Arabian way with the veil), sword dance, floor dance etc. You can check out my videos on youtube, there I have performances of all those different styles and stuff I'm talking about here
YouTube - Broadcast Yourself.
But I would never dare to tell that I have mastered the entire parts of all of those styles (except Greek Tsifteteli which is not such a wide field anyway
).
So I really think it is a matter of interpretation. On the other hand, if a dancers tells that she can do many styles, she should prove it, performing all of those styles and putting videos on youtube (or selling videos where she performs all of those styles), where the difference between the styles is obvious. Talking is useless, if you can not prove by doing what you are talking about.
By the way, have a look at my new video with fantasy veil dance: