Oscar 2017 Best Picture MixUp
So how could Warren Beatty and Faye Dunaway have been looking at that very same card, as the actor explained to the audience?
Turns out that for each category, there are two cards waiting in the wings, one on each side, as explained in a 2016 Los Angeles Times story by Valli Herman:
"In an undisclosed location, the partners tabulate votes and stuff two sets of winning envelopes, partly as another security measure and also to aid the show's flow. Stationed with their signature briefcases on opposite sides of the stage, either [PricewaterhouseCoopers partners, Brian] Cullinan or [Martha] Ruiz can dispense envelopes to presenters. At the end of the evening, each accountant will have given out about half of the envelopes.
"And the third set? 'There is no third "set" sitting somewhere that has the winning cards in the winning envelopes,' Cullinan said. However, the remaining, unstuffed envelopes and nominee cards are shipped to a second secret location, just in case some disaster prevents access to the completed sets. After the ceremony, unused cards and envelopes are destroyed by an industrial document-destruction company."