Another ballad often mentioned in the non-Child ballad category is 'Bramble Briar/Bruton Town' Roud 18, Laws M32. The story of course as Belden and Gilchrist have pointed out goes back at least to the Decameron. However I have demonstrated that the ballad need not be any older than c1750 (See my articles on Mustrad). Then again there is a strong likelihood that many Child Ballads aren't even as old as this. Another good case for inclusion on your site is that 2 American versions are by far the fullest versions extant, and one is the earliest extant.