Reviving this thread because there is a new piece on it, by Richard Jenkins. Katharine Briggs Memorial Lecture 2018, also published by 'Folklore'.

https://www.tandfonline.com/doi/full/10.1080/0015587X.2019.1585711

Jenkins references this thread.

Abstract reads as follows:

Abstract
This lecture explores the history of the British and Irish song family widely known as the ‘Unfortunate Rake’—which includes North American songs such as ‘Streets of Laredo’—from its earliest identification in 1911. Focusing on the contributions of Phillips Barry, Alan Lomax, and A. L. Lloyd, three widely-accepted elements of the folkloristic narrative about these songs are shown to be dubious, if not incorrect: first, the name itself, ‘The Unfortunate Rake’, is a misnomer; second, the ascription to the song of an eighteenth-century origin in Ireland rests on flimsy evidence, at best; and third, this song family almost certainly has no direct connection to ‘St. James Infirmary’. In closing, the implications for folkloristic knowledge and scholarship of the ways in which this misleading tale was constructed and the reasons why it became conventional wisdom are examined.