Gerry,
1. I was referring to the first parody as regrds Smut
2, everybody does not know that Foster was the original song writer
3 Plagiarism is presenting someone else's work or ideas as your own, with or without their consent, by incorporating it into your work without full acknowledgement.
4 Without the original song there can be no parody
so performers should, when doing parodies, acknowledge the original author, my experience of the uk folk revival is that acknowledgement is rarely the case