If you're doing a recording of fiddle tunes you may want to ask some other fiddlers about authorship/composing of the tunes. Some tunes that are thought to be old were really made up recently (Tunes like Nail that Catfish to a Tree was composed by Steve Rosen, though I think more than one person has thought that it was traditional). But I know some tunes have more than one title. So, it can be tricky. If you can find a tune in an old collection, you can probably assume it's public domain if it is from a source from pre-1923, as Joe mentioned. Another thinkg I have seen done is putting a notice on the recording saying that if someone can prove authorship of a tune, if you haven't found them, is to tell them to contact you for royalties. Considering you're talking about $45.00 for 1000 copies, it's not likely to break the bank.