I guess I'm old fashioned....if some-one is known for singing a particular song, then I believe that other singers should steer clear of it in that club or session. By all means sing it elsewhere...but not there!

I'm missing something here. We aren't talking about songs that the individual in question wrote, are we? If they're folk songs, i. e. in the public domain, they belong to everyone in equal proportion. If they're written by someone else entirely, who isn't there, then they don't belong to either individual involved - unless the author has assigned the copyright, which seems unlikely.

So how does one individual acquire a priority right?

Peter