PROOF that timelines split when Desmond failed to push the button?
Fact: we are explicitly told that when Desmond fails to push button = 815 crash
Season 6 pilot: The Flight Attendant gives Jack 1 bottle of Alcohol instead of the two that were shown in the "original" timeline. Season 1 pilot: Jack opens his eyes, gets up, and checks his pocket -There is only one bottle of Alcohol instead of the two that we are shown in season 1 subsequently.
The writers have claimed from the beginning that they knew where they were going with the show. To prove that they have been placing facts (like adam and eve, black and white stones etc) all along the show so that in the end when they reveal the secrets they can include these facts as part of the story to say "see we knew from the start!"
What better way to do that than …