In two of the stories, Watson throws down the paper as uninteresting and begins various trains of thought until finally settling upon one, at which point Holmes interrupts to agree that it is a ridiculous way to settle a dispute.
Watson is naturally amazed, but Holmes' explanation is simplicity itself.
Was the good doctor honestly confused at which adventure this occurred or in putting pen to paper had he forgotten that he had already related this incident and was so personally impressed by it that he wanted to ensure that he shared it with his readers?