I hope you will bear with me for a moment. There is a new documentary underway entitled, "Porchlight Sessions" which delves into the history and development of bluegrass and the instruments used. They are asking for donations in any amount $1 and up to complete it (needs to be fully funded by May 1). You can watch a trailer and the producer's comments (Anna Schwaber) at their site or you can go to Deering Banjo and (along with a couple of short articles about Earl, you will find an link to the Porchlight Sessions.
It looks like a great project; one that I hope they can complete. If you don't want to contribute, you might want to keep track of this effort and watch, or maybe order, the video when (if) it is finished.
Thank you - m