For what it's worth, I'm with you on this one Joseph--I've been reading John Fahey's "Charlie Patton". He does a very thorough analysis of music and lyrics, and points out that there is nothing musically, or lyrically that ties it exclusively to "The Delta", meaning that floating verses, rhythmic cadences and music figures are just like what was in music from everywhere else.

He also points out that Patton, who he says started performing prior to 1915, had a repertoire that included a lot of stuff that wasn't blues, where younger musicians, such as Son House and the Chatmons (who were his younger brothers) played mostly blues. This leads one to think that the blues might have become popular in Delta about the same time it became popular everywhere else--