It has do take the sum of all your runs into account. Anything other than that in a game designed to be played more than once with different outcomes and a completion % ticking up would be insanity.
yeah totally. likely when transferring over the game save, it only looks for like "Did the player extract person: X". etc in the save file. so whenever you did it, regardless of what run it was, it just ticks that off when it sees you extracting one of those specific people and records it when you complete a mission. sorry if it made it sound more confusing. but yeah don't worry about what rank you get :P
pretty sure 99.9% of all e3 parties are private and have guests lists etc. but seen many companies do giveaways for tickets. so likely would be pretty easy to get in by either emailing someone in the company or striking conversation at a booth or something.