IMHO it is generally impossible to define a "style" with precision, but it is possible to be clear on the derivation and modification of a song and its adoption in a community. Those are the facets of the 1954 definition and IMHO they are right.

I don't do much American stuff, but if I do do "Worried Man Blues" I often put in a verse of Amazing Grace (in the style of the Shepherds' Bush Comets) - if you see my point.