McGrath (Kevin, if I remember correctly from another thread), I partly disagree. I think we should make a difference whether there is an original version or only an earliest (known, printed). Songs like Three Score and Ten or Spancil Hill or Fiddler's Green have a known origin, i.e. have been written by a namable person at a specific time (and I remember how glad I was to read for the first time the original lyrics to Spancil Hill and to read the story around the song). For most ballads this information is lost forever and in these cases I prefer to read of "first known version" or "first collected by...".
Of course, 'original folk song' is a kind of misnomer, since the original version was not a folksong at the time of its writing. But the more correct 'original version to what later became a folk song' doesn't sound good to me.

Wolfgang