Thanks Jim...The problem with definitions is that the goal posts move too regularly. If you were to ignore Music Hall songs that have entered the tradition, then you would lose a good 30% of the songs in most collections. As a quick example, The Country Carrier, The unfortunate Tailor, Lamorna, immediately spring to mind. If we are to ignore stage songs from the 18th century we would lose another 50%, off goes The Rose Bud in June, Cupids Garden, Searching for Lambs, Green Bushes. The rest originated in Street Literature, or highbrow ballad literature. There is a misconception that a 'Folk Song' becomes less 'Folk' if we can trace it's writer. This therefore means that 'Folk Art' is less artistic if we know the artist.
Gypsy Ambrose Cooper rewrites Jimmy Rodgers songs with words of interest to travellers. One of his songs was collected with different words again, sung by Derby Smith. I'm afraid it's a Folk Song. It might not be pretty as Searching for Lambs. Is a Zoologist supposed to ignore Warthogs because they are not as attractive as Birds of Paradise. Then of course there are Rugby songs! Horrible sterile and loveless, just like the ballad Lambkin. I'm afraid subjective selection is our fate unless of course you are a Folklorist then God help you! Nobody else will.