I'm not trying to cast something in concrete, just trying to isolate one thing that has some modeately well defined meaning. We need some other categories as we get farther away from that towrd more modern 'folk' style all the way to Steeleye Span, John Denver, John Hartford, Phil Ochs, etc (newer ones I don't even know about). There's lots of borderline stuff I don't know what to do about. And then there's the touchy definition of what's a 'traditional singer'. Do we include old the time semipro entertainers that put Child ballads on phono records in the 1920's. How about the semipros like Obray Ramsay and others that recorded solos with their own accompaniment in the 1950's and early 60's. Jean Ritchie is a traditional singer when she sings her own old family songs, but the last two concerts I've heard her do were mostly her own compositions. Frank Warner was a collector, not a traditional singer, but he tried hard to imitate his traditional sources. He's about my ideal for an interpreter', and I think his son Jeff falls in the same category, as do Art Thieme, Lou Killen, Michael Cooney and a few other 'big' names.
Harry Ballafonte got much of his material from Caribean collections in the Library of Congress Folklore Archive, but I have no idea about how much he adapted it to be his own style.