It really looks like St James Infirmary Blues is a (slightly incoherent) amalgam of elements from several songs.

My thoughts on it:
- The "Old Joe's Barrom" opening may have been inspired by "Tom Sherman's Barrom / The Cowboy's Lament".

- The "St. James' Infirmary" verses about seeing his girl dying in the hospital may have come from Scarborough's "John Seley's Hospital" song (where the story makes more sense), or even from "The Bad Girls Lament / St. James Hospital", if we want to go back that far.

- The "Let Her Go, God Bless Her" verse makes sense in the various jilted lover songs it shows up in, but not in "St James Infirmary Blues" where the girl is dead.
It would make more sense if it was changed to "I may search this wide world over, but I'll never find another like she." but I've not seen it like that in any version of the blues.

- The funeral requests are an exaggeration/extension of those found in "The Bad Girls Lament / Unfortunate Lad", they make sense, if the guy is going to kill himself because he lost his girl and boasting about his gangster status, or if he's dying from a disease he got from his girl.
It's the sudden switch from the hospital scene to making his own funeral requests that leaves a gap in the story.
Porter Grainger's "Dyin' Crapshooter's Blues" first appeared in 1927, if I'm correct, so that can't be the origin of the verses, probably it's the other way round.