Snopes.com had a section on the John Denver/JW/Johny Carson legend and reports it as false. There are other versions with other performers and other groups of people, but the JW version seems the most common. I think if it had actually happened it would have made the news. I was around at the time and remember hearing it and thinking it was silly, as most urban legends are. People sometimes forget what actually happened and falsely remember the legend as having actually happened. Memory is not unchangeable. My husband and I gave a car to my son a year ago. They said we never gave them the title and we were puzzled, we both remember giving it to them. I even seemed to recall the color of the pink slip. What really happened is we couldn't find the title gave them a paperless title transfer doc, not the actual title. Apparently we forgot that, and that memory was altered and merged with an earlier memory of when we received the pink slip four years earlier.
I have been told many urban legends by people who swear it recently happened to a friend. I know that cannot be true as I heard a different version of the legend years before. That is why eye witness testimony is almost useless. After a robbery, you could ask ten people and get ten different descriptions of the suspect. At best you could find some detail that most agree on. If those ten people then discuss it among themselves, all the stories will change to be more like whoever is the most sure of their story. The others will then be convinced that they remember that detail and it will become part of their "memory". They will be convinced it actually happened and will be offended if you doubt them.