When Bull looks at Walt Hyland's duplicate ring-bound diaries, the shots from his POV show both open and clear. However, in the longer shots, facing Bull, there are two red-bound books lying on the left-hand (from Bull's POV) diary, one on each side, completely obscuring the pages.
How would the saboteur know which parachute the Governor would use? He would've had to tamper with all of them.