Add to your list of pros Danny Farmer, Don Remien, Rick and Patti Roberts, and Jim Kappes.
Billy Sargenti grew up with Rex and of the pros mentioned had vastly more exposure to him. The amateurs, Lanse and Dana Brown, Judy (Weikel) Aycock, Rick and Patti Roberts, and Delma Hazzard to name a few had significantly more time with Rex than any pro except Billy. Rex's notes were copied and widely distributed but as anyone who was around him over a long period of time can attest he was subject to change as happened most visibly with selection.
Beyond Rex's immense primary contributions to dog training came the secondary ones passed by some of the above to the next generation of trainers e.g. Dana to Remien, Judy to Danny, Kappes to Lardy etc.
Dr. Ed has identified a key often ignored contribution. Rex's 2nd generation protégées!! And I daresay there is a 3rd generation now! There are tons of notes floating around, some from Rex, some letters to clients and most by his students.
Rex was constantly changing details, based on the record of notes andthose who knew him. His standards and passion for the dogs never changed. But the Rex Carr on the Carr/Rorem DVD is quite different than the earlier Carr.
I suspect extremely few really understood Rex and his lateral thinking and insight into dogs. Perhaps Judy Aycock came closest and at the end Rorem, who became Rex's major pass along disciple, along of course with long time student Sargenti.
As Dr.Ed identified Lardy learned Rex's program steps from Kappes but Mike did a study visit with Rex in the late 90's. He tweaked the BB Blinds and Tune-ups to what many of us follow today. In my study visit to Rex, with Rorem, I learned much and refined my training. Drills like my swim-by tune-up and cast into water drill and water tune-ups had their genesis from Rex.
I, like others, who have much more experience, with could go on and on, but I fear there will never be an accurate chronicle of the real story about Rex including all the evolution and game-changing developments!!
PS. There is an audio tape of a Rex Carr workshop in the 70's in Colorado! It is gold. Try to find it!