At 20:55 David tells Marcy he didn't know why Ken changed his mind and did not fire David. But before Marcy was reset she had already told him she talked to his boss and straightened everything out. The post-reset Marcy would not know about that, but David should remember it.
In the opening scene, Carly's rifle has the bolt open. The lever is obviously pointing up. It is impossible for the rifle to fire when in this condition. Also, she is not holding the rifle steady at all. A long distance shot like this would require her to lie prone with the rifle stabilized on a bipod.