El Greko,

To date, I have never heard a version of one of my songs that was an improvement on the original. Now, there are many people who play instruments better than I do, and some who sing better than I do, but there are few who write (or rewrite) my songs as well as I do. I usually do not release a song to the public until it has attained its final words and tune. In the one recorded version of one of my songs that I know of the rhythm has been butchered such that the song cannot be learned correctly from the recording and the words to one verse have been changed. Beyond that, someone who heard that recording contacted me to say that he had made up a couple of new verses and he could imagine people making up a lot more of them! (I was horrified: the original is an -- intentionally -- short song about the fleeting nature of time together)

I am delighted to hear that others improve your songs and I await the day that that happens to one of mine.

As for Mr. McCartney, members of the Beatles had that rare privilege that songwriters long for: they got to establish their version of their songs as the standard version long before other people had their way with it.