LL- the way I understand it is that all TOS is Brachialplexopathy, but not all brachialplexopathy is TOS. Thats b/c the BP turns into all of the nerves over there. I think.
One other thing to look into is called "double crush." I thik that the best way to describe that is that you have 2 smaller impingements on the nerve that, independently of each other, aren't a problem, but together, they affect you.
Feel free to correct me!