This question can't be answered, for the following reason.
Imagine you somehow had time (and inclination) enough for the following exercise.
You start by picking a song that definitely IS a 'folk song' - a traditional country song from the 17th century, perhaps. This goes at the top of a list.
You then choose a song that definitely IS NOT a 'folk song' - maybe a modern heavy metal track. This goes at the bottom.
You then make a list of all the songs you've ever heard in your life, grading them according to whether they're nearer to one or the other of your 'folkiest' and 'least folkie' songs.
Then, using your best judgement, you decide where, among the countless songs in your massive list, to draw a line: all the songs above the line ARE folk, all the songs below ARE NOT.
But, the 2 songs each side of your line would have virtually the same amount of 'folkiness'. The 25 songs each side of your line would. Anyone could look at that list of 50 songs, 25 above and 25 below your line, and say, "Why on earth is this one folk, but this one isn't?"
And furthermore ... if 99 other people carried out the same exercise, their lists would almost certainly be vastly different from yours. How could we ever decide which (if any) of the 100 lists was the correct one, before we even begin arguing about songs above and below the line?