Hi jag
I don't think anyone is saying all of this is cut and dried. There are many overlaps and grey areas. However most of the academic pieces I am avidly soaking up seem to suggest (and Jim is also saying it if I read him right) that what went on in families and communities when the songs were passed on orally/aurally can no longer take place in anything like the same way as it did prior to say 1920 (arbitrary). There is no cut off point as it was gradual process. Nearly all of those survivals are gone or will be gone in a few years. (We can argue about a very few possible exceptions) but this is the general situation. One thing that has replaced this (and it is just one thing) is that thing set up and known as The Folk Scene, or the second revival, which ought to be considered as perhaps a new tradition with new methods of transmission.

Apart from that who knows what researchers in a century's time will make of it?