As written the song was obviously a comic piece of the 17th century. The change to the mysterious Foggy Dew is most likely a conscious rewrite, although gradual evolution shouldn't be ruled out just because we have no intervening versions. One suggestion: 'Bugaboo' sounds too much like 'bugger boo'. How old is the word 'bugger'? Bob Thompson set the appearance of the 'Foggy Dew' versions at 1775 or a little before that, as printed by the Dicey-Marshall dynasty in London.