I swear I am not just a guest!

I have been given the unenviable task of researching the pieces that comprise the songbooks used by my dulcimer club. We're trying to weed out songs that are still under copyright so we don't end up sharing a lot of stuff that we shouldn't be sharing. I've had pretty good luck finding authors and copyright/publication dates in my old song books and on the Mudcat and Cowpie databases, but does anyone know good sources for this information, especially on songs that don't have lyrics? We have a lot of waltzes and bluegrass tunes that make me suspicious.