The difference with the broom analogy here is that anyone would be able to see the modern version is recognisably the same song as Bickerstaff's 18thc text.

Here is an honest opinion, even the modern-day tune is quite unlike most traditional tunes. In fact it is very like the pieces that came from the glee clubs of the early-19th century, pieces like the Copper Family's 'Spring glee', 'Dame Durden'......

Jim, what makes folk songs folk songs is the PEOPLE selecting and shaping. The origins have sod-all to do with it.

Regarding the 'Cornish' connection. 'The Sweet Nightingale' text as we now sing it was published in Bell's 'Ancient Poems, Ballads and Songs of the Peasantry of England' in 1857 where it is described as 'An Ancient Cornish Song'. The early anthologists were apt to use the term'ancient' very loosely and with no real research. 'This curious ditty which may be confidently assigned to the seventeenth century' etc. Bell heard it in Germany in 1854 sung by a troupe of Cornish miners on stage (no doubt in the form of a glee).

All of the many other versions derive from Bell including various publications by Baring Gould who collected the tune from various Cornish/Devon singers and published it in Songs of the West in 1905. Cyril either got it from Songs of the West or from Canow Kernow in the 1950s