IMHO a lot of folk music is a telling of the social history of ordinary people, tied in with the great events that touched them. Those songs were sung and handed down. The successful ones survived but I am sure that there were a lot that didn't.

In the past century there have been songwriters who have blended into the folk tradition, mostly writing songs about events, ancient and modern. I'm particularly thinking of Tom Paxton, Gordon Lightfoot, Gordon Bok and one of my favourites, Utah Phillips. Some of their songs have caught the ear of 'folkies' who then take the songs up and spread them around. Those songs actually say something about life as it is lived and are generally more than just a complaint about how hard it can be or how unfair it is.

If a song is contagious in folk circles it becomes part of the legend, whether it be 200 years old or 2 years old. The critical fact is that it must be a song that people WANT to sing. I think that is the difference, maybe, between folk and other types of music. How well does any song translate when sung without benefit of mikes and recording equipment? Does it need full on musical backing or does it stand alone, sung accapella, or in harmony?

I've sat in sessions where the 'singer songwriter' regales the audience with his latest gem. Unfortunately, all too often these 'gems' are unsingable and do not sit well upon the ears of those listening. They ain't going to end up in the tradition any day soon.

Anyway, that's just my personal opinion