[jman220]

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all that time no one ever showed down two of the same card after he was continually switching them? I doubt that very much

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You're misreading the OP as well. It says he took cards out of play, adn then put them back into play. This would not cause duplicates. So the deck was perpetually short however many cards he had up his sleeve, and since there were no automatic shufflers which count the deck, this wasn't discovered.