Arkie, how can you "verify that music performed is in public domain"? If they have a copyrighted version, how can anyone prove they didn't get at least the words and tune from that version? I'm starting to do small gigs where I play mostly parlor and music hall songs. In general, my rule of thumb is, "if it's in the Levy collection, it's public domain," at least for the words and tune. (All zither arrangements are my own....)

So. If a song pre-existed a particular copyright, what does that mean for performers? Can we sing it in versions that were published before the copyright? ???