In folk music and folk song the words and tunes constantly get borrowed/develop/change over many years sometimes because of faulty memories, sometimes because an individual preferred his/her own phrasing and sometimes because collectors bowdlerized the lyrics or a fiddler added and extra bar or two.
I expect that many of the oldest songs would sound very different if we could hear them today.

For me that is what makes much of folk so interesting wherever I hear it.