This is my understanding of the pure folk music
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The term, which originated in the 19th century, has been defined in several ways: as music transmitted by word of mouth, as music of the lower classes, and as music with unknown composers.
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Therefore based on that, what isn't folk gets a bit easier.

This is an example of a song that many people believe to be traditional, but isn't as it was written in the 1960's and the person who wrote it is still alive and a Lincolnshire Yellowbelly. However this song is as good as any traditonal song. It was recorded live in March 2010 by Mudcatter Sooz, at Faldingworth Live and a great job she did of it.

http://www.youtube.com/watch?v=3-yzh8bO6PM

It's quite strange, but a few weeks ago at a local singaround that I Mc'ed, John Conolly came along and I asked him to finish off the evening with Fiddlers Green. He explained all about the song etc and then sang it.
A woman sitting next to me, who was Irish, was singing along, who to my knowledge, was not really a folky. Afterwards, I asked her how she knew the song. She said that she and her family sang the song often and until this evening, had always thought it was traditional and had no clue to the origins. It came as a big shock to her, to be sitting in front of the person who wrote it and was singing it.

Is that the sort of thing you are looking for Foulestroupe?