I'd say those more dubious, in that they are the products of professional musicians. Early Blues not entirely or altogether so.

Of course, as so often, there is that wide border between folk/not·folk -- the Debatable Land of folk music. But I should personally say that Mance Lipscomb, eg, was far more tending to the folk side than Scott Joplin or Satchmo [even if he did invent that bloody horse!].

Again, let me stress -- a taxonomic, not a qualitative, distinction.

≈M≈