Reading between the points scoring, the nit-picking and the insults, there have been many good points made here. However, to the main questions raised here there is probably no chance of getting an agreed definition and there never will be.

I remember - decades ago - a very late night at our house when Bert Lloyd was staying with us after he had performed at our folk club and I was trying to draw him out on a definition of what constituted the tradition in song and singer. He sighed and said, "Look out of the window.... we can both agree that it is the night. At breakfast tomorrow, we can both agree that it is the day. But don't ask us to agree on the exact point where one becomes the other because we never will. Just listen to as much of it as you can and then use your instincts."