Jim,
We seem to be saying the same thing. I'm well aware the situation with travellers is very different and that in parts of Ireland until recently there was a strong LOCAL tradition of song writing, having read the likes of Glassy, Sam Henry, John Moulden, Hugh Shields etc.

I had assumed we were referring largely to the corpus of traditional songs common to the British isles, North America and a few other English-speaking parts of the world. I'm also very aware that the process between oral tradition and print was a two-way affair in some cases. The broadside printers, or their hacks, were very commercially motivated (as were your travellers described above I might add)and if a song was popular, as Mikeen said, it soon found its way BACK to the presses. Having studied and compared many many texts I am still convinced that the vast majority started out as commercial pieces with a view to a sale.

Of course we can't name the vast majority of the authors. Nobody cared who wrote them and they only got a few pence for writing them, by the 18thc.
However I could write you a list if you wish of those that purport to have authors.