A further thought, the mechanical copyright in a recording - that is the right to make copies of that recording, belongs to the person who "facilitated" the recording.
In other words, if a record company books you into a studio to record a demo,, they have the right to make copies.
If I let you record free in my studio, I have the mechanical copyright.
If I record in the College studio, the College owns the right to make copies of the recording.
This is completely separate from the composers' or arranger's copyright, and performer's copyright does not exist.
In my opinion, copyright paranoia of a major excuse for never getting your music out there.
What is the point or profit in holding copyright in something nobody has ever heard?
As for your Compilation problem, see a lawyer and get a single song deal set up. As soon as your track is mastered onto a compilation CD, a whole new ballgame opens up- because it is not entirely your track any more.
Cheers
Dave