When I was running the 'Liar's Bench' in "Messing About in Boats" I found that there are very few new stories. In fact, the only new "folktales" I was able to come up with were ones that actually happened to me. Otherwise, sooner or later I would run across a citation or the ur-story in another source. It go to be downright embarassing after a while and led me to give up on the column for a while.