Dave O, way behind the times, approx. 1954, to be more accurate. Known authorship is quite rightly totally irrelevant to any meaning of folk song except perhaps your own. It was originally in the IFMC 'definition' but immediately dropped on the grounds that it's silly and indefensible.

For instance a folk ballad like 'The Demon Lover' is folk but ceases to be folk because we now know who wrote it. Daft I calls it! There are numerous other examples.