Thanks Mr. Book Binder and khandu.

I received an e-mail from Dick Waterman, and he said he doesn't believe MJH and EC every shared the stage together. He said Libba was a very shy woman and didn't mingle much with other performers.

I also posted my query on rmmga and received this very interesting (and plausible) reply from a Jon Pankake:

Many nineteenth-century "parlor guitar" instruction books survive that taught one to play the bass strings with the thumb and the treble with the fingers. "Spanish Fandango" was one of the pieces taught and both EC and MJH played versions of it. When Hurt was a boy an itinerant music teacher used to board at his home and John could well have been exposed to formal guitar playing. Not to say that either Hurt or Cotten used books or were formally taught, but their style of playing was in the culture and influenced players at all levels of the culture. For example, every tuning that Robert Johnson used appeared in parlor guitar instruction books long before his time.

Does anyone know where I could find a reproduction of one of these parlor guitar instruction books?