That's interesting. So Burns published a song that he wrote the words of, to the old tune, which had nothing to do with the Rev. Williamson story, but it has been largely ignored by folk singers; and also possibly wrote but probably just collected an extremely bawdy version of the "curly pow" song; and Burns was clearly aware of the story about the Rev. Williamson. This extremely bawdy version then presumably morphed over time into the moderately bawdy version that is still widely sung today and which is in DT without attribution - have I got that right?

And presumably the reason that the Burns version has largely been ignored despite being good poetry, while the moderately bawdy "curly pow" version has survived and is still widely sung today, is that the Rev Williamson story caught people's imagination, whereas the Burns version doesn't have much of a story to it, so most people prefer the traditional song to his lyrics for that reason.