I have a piece of music with a working title and no lyrics.It was written some 30 years ago by a couple of friends of mine with whom I have written several songs. They have lost interest but of course, they still get their credits as they should. I have copyrighted some pieces in the past, but I never did for this piece because it is unfinished. Can I still protect it with a copyright and then update it in the future with lyrics and a proper title? Or does it then become a separate copyright and/or a separate work? I want the song protected, that's the main thing.