"I've been thinking about Cecil Sharp's statement, that a folk song is always anonymous."

In some respects Sharp was a scientist who had a scientific view of his collecting activities. What fascinates me is that he attempted to apply Darwinian evolutionary theory to the study of folk song. But no scientific theory is ever the last word; there are always exceptions and if enough of these build up then the theory has to be modified.

The people who built the 1954 definition realised that the bit about anonymity of composition didn't fit so discarded it - there's no shame in that! The theories of people like Newton, Darwin and Einstien have been modified by those scientists who came after - it's in the nature of scientific theories.

PS: "I like folk music and I like rock music, therefore rock music is a form of folk music" doesn't qualify as a scientific theory!