I know that there was a very big push to get people to buy advance tickets for months. It's difficult for many to be able to keep appointments that far in advance. Just a personal example, my aunt and uncle were supposed to go see it on July 5th, the day after it opened. But my uncle hurt his knee playing ball on July 4th and didn't feel like going. He couldn't exchange his ticket for another day and couldn't find anyone who wanted it. But the good news is that those who bought advance tickets but didn't use them will most likely buy new ones, just because they're determined to see the movie.