The kiss is a cursed kiss anyway, so the sense would be the same either way. And I've heard it sung thistle too.

But once a song gets out into the oral tradition - which means people singing what they have heard (even if on a record) and remembered or reconstructed, rather than what they have read on a page, the notion of a definitive version gets rapidly eroded. Indeed it seems toi me that the existance of variants are a token that a song is alive.

And the fact that an author has settled on a particular set of words on their website doesn't make that "definitive". Writers have always revised and changed what they have written, and the latest version isn't always the best or the one subsequently preferred - William Wordsworth is a case in point. Bob Dylan is maybe another.

Sydney Carter took pride in constantly changing his songs, not with the idea of improving them but to keep them fresh. (Though maybe part of that was that like a lot of us he had a tendency to forget the odd word or line and had to improvise an alternative on the hoof - and sometimes found that the change worked better.)