IMO, this is pretty silly. If it weren't for collectors, Dick Gaughan wouldn't recognize a river if he fell into it. And if it weren't for collectors, folk music (whatever that means simply wouldn't exist as a genre.

Nobody says you have to (or, more importantly) are able to sing exactly what's been collected. But if nobody sees or hears what's been collected, there's no basis for your music (unless you consider the pop folksingers as a source, and they've been collected by record companies).

There's no right way to sing a folk song. But dammit, there are a lot of wrong ways.