And here is a tune for "The Bad Girl's Lament" (here called "Annie Franklin") collected in Newfoundland in 1959, which is precisely the familiar "Streets of Laredo" / "Bard of Armagh" tune.

http://www.wtv-zone.com/phyrst/audio/nfld/15/annie.htm

Pamela, be ready to answer the question of why certain aspects of the "folk process" are held to differ from simple "plagiarism."