Karen sent me this link to Motherwell:

Little Mushiegrove

It looks from that as if the song had fallen out of tradition on the English side of the border (or Ritson would have noticed it). There are slight differences between Motherwell and Chappell - if anything, Chappell makes it sound more Scottish than Motherwell did. Karen says Chappell's publication of this song predates his feud with the Scottish musical establishment, so there may not be any ulterior motive behind him cutting Motherwell out of the narrative - but his version is so closely related he has to have got it either from the same tradition as Motherwell or from some oral retransmission of what Motherwell printed. Since this was 200 years after the song was written, not far from the border, tunes it was sung to can't have been very definitely from one side or the other.