The Dylan quote that started this thread 5 years ago was, "Folk music was a strict and rigid establishment. If you sang Southern mountain blues, you didn't sing Southern mountain ballads and you didn't sing city blues. If you sang Texas cowboy songs, you didn't sing English ballads. It was really pathetic. You just didn't"

That didn't really apply in the days that Dylan was starting out any more than it does today. The Even Dozen Jug Band included Bluegrass players (David Grisman), Blues players (Stefan Grossman) future rockers (John Sebastion)...
Jim Kweskin's group was similar having Bluegrassers (Bob Siggens and Bill Kieth) and blues players (Geoff Muldaur). Kwesin himself recorded tunes by such different players as Grandpa Jones and Blind Blake and Hoagy Carmichael.
Joan Baez, Tom Rush and Ian & Sylvia did British ballads, blues and country. All of these players were contemporaries of Dylan.
Dave Van Ronk sang English ballads and blues. Pete Seeger did songs from a wide variety of genres, Woody Guthrie sang old country tunes (Carter Family tunes formed the basis for many of Woody's songs) and old blues tunes (House Of The Rising Sun). These were some of Dylan's mentors.
I'm sure there were some musicians who were "strict and rigid" about their material, but it obviously didn't apply to the whole "Folk music establishment".