I must be selective - I have the rest of my repertoire to get through, etc.; so, Howard: if we know the author of the song/tune it is NOT traditional, and we should give credit anytime we sing/play it.
It may help to consider folk, in England, e.g., being divided into 2 branches - traditional and composed (rather than contemporary for temporal reasons). Given that, the only ways any knew trad. songs will be created (as opposed to oldies being rediscovered) is through a lie or suchlike - perhaps someone could create a song, sing it at a folk club, and claim to have forgotten where and who they picked it up from; others like it, learn it, and it becomes a trad. song. Ewan MacColl's fine folk songs, though, will NEVER be traditional songs - due to rights, technology, etc., it will not be forgotten that he composed them; they, rather, belong to the composed branch of English folk songs. (And neither will they ever be called gobbledegook.)