Also curious about this one, as I've long wondered whether Jerry got his inspiration directly from (Bill) Monroe, or from generational contemporary followers... guys who worked for Monroe, like Peter Rowan for instance. Those little extra measures happened quite often in his music, and they would have had to learn that. These days, it usually gets kinda' auto-corrected out of mainstream bluegrass.
Interestingly enough, I have also been borrowing from Oteil's lines on
"Cold Rain & Snow", but just because I like them and they work for my particular need.

(my source, FWIW, was the MSG show on 11/1/19)