It may just as easily be borrowing, either from "The Streets of Laredo" branch (brought to public attention in America by Lomax in 1910) or else from "The Unfortunate Lad/ Rake and a Rambling Boy" song

'Rake and a Rambling Boy' is a different song ('Flash Lad' etc) but, yes, I agree it looks like a borrowing (and 'Streets of Laredo' is a good candidate) - but isn't borrowing one of the processes we're talking about here? If it is a recomposition it adheres to the original template quite closely.

As I say, the "Blues" is an "offshoot," not a lineal descendant, and surely it's the result of almost total recomposition.

If recomposition means it's not a 'lineal descendent', where does that leave the 'Elfin Knight / Cambric Shirt / Acre of Land' family, for example?