Peoiple often speak in a non-rigorous shorthand: eg "Dutch people are taller than Welsh people" (obviously, you need to add "on average").Sharp's statement on the anonymity of folksong should be viewed in that light. A more appropriate version would be "Folk songs are considered anonymous and common property, by the folk who made and sing them". The point is, people singing the Farmer's Boy have not in general been thinking "This was written by X" Clearly, the status of the Farmer's Boy as a folk song does not really change if diligent academic research turns up a putative composer(though the research may not give an accurate result, anyway). It is just a question of attitude. "Searching for Lambs" is a folksong. "Yesterday" is a Beatles song.Simple.