"If 'Little Boxes' and 'The Red Flag' are folk songs, we need a new term to describe 'The Outlandish Knight', 'Searching for Lambs' and 'The Coalowner and the Pitman's Wife'."
Folk song proper is far too old in the tooth (another of your "old geezers") to re-identify itself - "

Yes, but...

The term 'folk' is understood by most people to encompass both. 99.9% of them have no interest in the difference between them. Unfortunately perhaps, the meaning of words is determined by usage and cannot be dictated. "Gay" is the obvious modern example of a word whose common meaning has changed utterly - "disinterested" is rapidly coming to mean "uninterested", and "momentarily" is starting to take on the American sense of "in a moment" rather than "for a moment". This is annoying for those who would prefer to use language precisely or who now lack a word to replace the original sense, but you can't turn back the tide. Popular usage creates language just as it does folk song.

I agree that for the relative few who do regard the distinction between "Little Boxes" and "The Outlandish Knight" as important, a different word is needed. Since 'folk' cannot now be redefined, better to find another term such as 'traditional song' to describe the latter. This is still 'folk', so you won't need to re-bind your books, but it forms a sub-set of the wider meaning.