Wait wait. A song of known authorship's not traditional? Usually not, I agree, but what about, say, Alfred Williams' 1907 "A Man Without a Woman" (Roll a Silver Dollar)? William S. Hays' "Curtains of Night" (I think), Tucker's "When This Cruel War Is Over," Dan Smith's "De Boatmen Dance," Samuel Lover's "Bold Sojer Boy," Keith's "Go 'Way Old Man," Tyte's "My Mary Anne?" All these have been collected in various places from impeccably traditional singers and communities. And then there's Ben Jonson's "Drink To Me Only," which has passed into tradition with three different tunes...

(Not the best examples, I know, but it serves. I'm sure I could think of better ones if I wasn't in a rush. I'm just not sure "traditional" excludes known authors.)

Bob