Perhaps there was a second best actress card in error. I read several years ago, that only one person in the accounting firm knows the winners. He is required to memorize the winners in case there is a mistake and this person is backstage watching.
At this level, there shouldn't be this type of error. Should be, as Rush says, double sourced and triple checked. Whomever that 'one person' is at the accounting firm should have gone over these envelopes many times. Letting two envelopes go that were exactly the same is highly suspect.