" but certainly a lot came originally from professional, commercial song writers."
We know that some probably did, but we don't know how many.
Our knowledge of the traditional repertoire prior to 1899 is virtually non-existent, and we have only a scanty picture of what was around after that.
It really does take more than tracing a song back to it's first publication date to claim an origin.
Many Child ballads have been preserved by non-literate Travellers - rarities such as 'The Maid and the Palmer', 'Lord Bateman', 'Young Hunting', 'Lord Gregory', 'Lambkin'.... have been recorded from Irish Travellers in the past 30 years.
We recorded extensively a non-literate Traveller who took his non-literate father's songs to a printer, recited them over the counter to the printer who then produced them on 'ballads' song sheets which were being sold at fairs and markets right up to the 1950s
We have talked to settled singers about their attitude to the printed word as far as songs are concerned - extremely complicated.
One of the big surprises we have had in Ireland and among Travellers is the large number of anonymous community composed songs which bacam part of the local repertoire but never made it anywhere else because of their parochial nature.
We know that this was the case in Britain among cotton workers and other industries
Man is a natural song-maker - there is no reason to assume that he relied on the printed word rather the the other way round - that notoriously poor poets (hacks) should have invented our beautiful folk songs from scratch rather than lifting them from an existing oral tradition and adapting them for selling.
Unless scholars take all these, and many more factors into consideration, I strongly believe thay have no right to make claims that 80 - 90 percent of them started life on the broadside presses      
We were told a few weeks ago by a 90-odd year old singer "if something happened, somebody made a song about it" - I don't believe you can say plainer than that.
Jim Carroll