Exactly why it was staged. No way in hell that shit was an honest mistake. What if he was given best actor in a leading role and announced Manchester? It had to be the huge fav where they pull your leg for. These actors are all millionaires. No one should feel slrry for them. It's entertainment. Plus what are the chances you accidentally give the duplicate to Warren Beatty. If they make duplicates of them all then that just makes it even more unlikely for it to be a honest mistake at the most dramatic part of the night. Entertainment.
I read an interview with one of the PWC accountants done before the Oscars - apparently duplicates are made for each envelope - There are two accountants who bring the envelopes separately to the event in case one gets delayed or some other reason. So It's completely plausible this was just an mix up and he was given the wrong envelope.
You could tell Beatty was confused after reading it and when he showed Dunaway she just blurted out La La land with reading it closely.
I actually think it was handled pretty well on stage from the producer of LA LA land giving back the Oscar to the explaination of Warren Beatty.
If you watch the show - As soon as they Announce LALA Land as the winner the PA announcer starts giving the LALA LAND info - it was a total mistake....
Too Bad it happened