” But you do not ask the obvious question.... which John? John the Presbyter? John the Evangelist? John the Apostle?”
Not an important question since all three names may refer to the same man. But assuming that each name applies to a different individual, just to give your latest straw a chance, they were still three first century Christians close to the events that had just transpired.
It’s only within the confines of your little game of telephone that it would be hard for a first generation to pass on their knowledge to the next. In the real world I’ve never seen a teacher who whispers his knowledge to a student in one sentence and then tells him to pass it on. I always experienced that as a child’s game. Your experience evidently is different, which should explain why you think that argument has any merit.