What seems to have happened is that Mosconi missed on ball number 527, he said it happened that way. Then as the years went on when asked about it he started saying that he simply quit (more mystique that way) and as one poster on another thread said he started to believe that he never missed. I've heard that Charlie Ursetti witnessed Mosconi run 589 or thereabouts in practice and he says Mosconi just quit to end the run. maybe Mosconi just incorporated that into his 526 run, mixing the stories up. Who knows? But I have to believe he missed a shot to end the 526, I just can't imagine anyone writing in a book that they missed if it wasn't true.