Some Marginalia:

Cecil Sharp collected Swannanoa Tunnel in 1918. He had some trouble with accents, and wrote it down as Swannanoa Town, O

The interrelationships of various "Roll On" songs is covered pretty well in Only a Miner (Archie Green). Good book.

John Garth, an a discussion at the Ballad-L list, brought up the point that flesh-and-blood bulldogs don't bark; made a convincing argument that "bulldog" in many songs referred to a style of revolver,