How about 'Lord Soulis'... it appears in Scott's Minstrelsy but not in Child and, according to one person to whom I have spoken, was possibly in the repertoire of the Borders singer Willie Scott.

Maybe Willie Scott could have got away with it if he was singing in a pub where all the roads out were blocked by a blizzard. That one fails just about all of Child's criteria for inclusion. (If Stephen King had edited the Child collection I'm sure it would be in there).