Be interested to see your compilation version, Phil. I too have put together a compilation based on the English versions, but more for study purposes.

my opinion based on many other ballad adaptations is that the Scots took a mid-18th century English broadside (not currently extant) and added in the supernatural bits etc. Think Scott's extra supernatural bits for The Daemon Lover, or Scott's extra bits to Douglas Tragedy based on Earl Brand, Scottish adaptation of Lord Thomas and Fair Eleanor, Peter Buchan's 'Bonny Lass of Fyvie' adapted from 'Pretty Peggy of Derby', etc.

One thing that adds to this idea is that the English versions, seemingly without the help of multiple rewritten broadside versions, has produced quite a varied selection of multiple versions, suggesting that it had been in oral tradition for some considerable period such as a century and a half. This fits in with other ballads from the mid 18th century that did not get multiple adaptations in the 19th. Not many but there are some.