To be clear, some doctoral or post-doctoral research evidencing precisely how effective 'the process' is as a way of defining what's commonly described as folk music would be most welcome. I have no problem with change as a vehicle of transmission, I hesitate to bracket all folk songs as substantially changed because the index of transformation is not defined in a meaningful way. Taken as a whole my instinct is some traditional music is clearly common whereas others appear to be taken as common music on trust.