Character mistake: After Stewie and Brian go to tell the past versions of themselves not to tell 1999 Brian about 9/11, Stewie then finds out that Brian then told 1999 Brian to write the Harry Potter novels. This would have been impossible because the first Harry Potter novel was published in 1997, 2 years before the time period Stewie and Brian arrive in. (00:16:35)
Character mistake: In the cutaway gag involving George and Lorraine McFly from "Back To The Future" Lorraine says she hasn't seen Marty from high school since prom. George, Lorraine and Marty all attended the Enchantment Under the Sea dance in November 1955, not the prom, which is usually held in the spring.
Character mistake: When the family is about to drown in the panic room and start arguing with Peter about not liking "The Godfather," Chris starts listing off the great actors in it. "Robert DeNiro, Al Pacino, I mean, you've never seen...ROBERT DUVALL!" Robert DeNiro is in "The Godfather Part II," but not in the first one. (00:19:30)