I watched an interview taped sometime ago with SRV while he was extolling the virtues of Colin James (much younger then) and his prowess in country and Delta blues history; his comment was that Colin had a better understanding of the roots and history than he had, now that's quite a humble admission. The fact is that Blues gurus are everywhere and their existence is an immeasurable asset to the inspiration and creativity that keeps building on foundation techniques of the old greats and masters to create new variation and new directions for the blues while cloning old tunes with a twist, giving new life to the musician's music (Blues), for each new generation.
I guess the key is to listen to that old stuff, the stories, the names (many forgotten; case in point from a recent Winnipeg Freepress article Jan 24 sec.D4, on " Down-on-their-luck bluesmen find help at tiny farmhouse"). These old and not so old guys stretched in different directions whooped and hollered, squeezed impossible sounds from a harp and despite tooth decay, blindness, speech impediments; soothed ears with great music. Who knows of these guys? Most never made it to the big time, some never recorded, but there are the stories, the chicken scratches that are collected and filed away by the likes of Ralf Abramson,  Poor Boy Rodger, Colin James etc. and that 's just a few from the prairie provinces. Sitting down with these guys and just soaking up the stories is a special event, just ask around the locals at blues gigs and jams, there's always a guru close by .... start out by saying did you know Big Momma Thorton did  "Ain't Nothin' but a Hound Dog"?
Bob