Genuine question here as I do not know - Once the song is out of copyright and can be altered and absorbed into the "unwritten living tradition of a community", can it be said to be a folk song then?

As an example, the song 'Blue Moon' is sung in an altered form by a very large community - Manchester city fans! Can that be classed as a folk song? Our resident band at Swinton also incorporated the tune into their version of 'Nancy Whisky'. How does that work in terms of the folk tradition?