Don't know what you mean by firsthand knowledge, Sourdough, but I saw Doc Watson for the first time at the home of Alan Lomax on w. 3rd St. in New York City when Doc was playing behind Tom Clarence Ashley. I remember thinking that he was as every bit as good as Ashley and had a very commanding ability for being relegated to the role of accompanist, which he was at that time. I think Alan was recording them there. "East Virginia" and the "Coo Coo Bird" had always been two of my favorites and I think I got interested in the modal banjo tuning through hearing Ashley. If you raise the second string of the five-string banjo, you get a suspended second which doesn't contain a third in the chord and this enables you to sing in major, minor or modal scalar songs. I think Ashley may have been one of the few to employ this tuning extensively. Don't know whether he invented it or not. The frailing style played at the bass of the neck rather than over the middle part of the drum was unique as well. I don't remember hearing too many banjo players do this. Buell Kazee was one. John Cohen was playing in that style in those days (1963 or so). Later, Fred Cockerham and Tommy Jarrel played more intricate melodies using somewhat the same frailing style.

Seems like I recall Doc wearing suspenders, then. Ralph Rinzler played mandolin in the Greenbriar Boys, a folk style bluegrass band.

Frank