Indeed I have heard other changes which I did not like, or not enough to adopt them. But I would not call the amendments by other artists "co-writing" (what are you trying to do to me? they'll be wanting royalties!), in that this was not an agreed or conscious partnership in the writing of the songs - and the fact that they are well-known does not exclude them from being part of the folk process.

Well put, George (LOL) :-)