@Jim Carroll. I don't think "Fakesong" is about what the collectors brought back but about how they theorised about it.

There are many context where people have to theorise. Collectors who just collect and describe can only go so far. A butterfly collector who just collects and describes will never be regarded as a scientist. Sharp, to discuss things with his middle class pals, give lectures and promote the songs into schools has to have theories to talk about. Similarly Harker, writing a book published by an academic publisher, can't just give us all the ordered results of his reading - he has to have a theory. Bearman was doing it as part of a research training that would prepare him for the academic world.

There are places where theorising is optional so long as the research is good and readers are interested - many articles in Folk Music Journal are like that.