Other mistake: Part 3 - The Betrayal: Fran tells Stu that she's pregnant on July 19th, and the way she tells him implies Stu is the father, and she's due in January. It's impossible. They didn't even meet until early July. Counting backwards from January, nine months lands in April. Way before the super flu even escaped. Way before the movie is set. (00:05:45 - 00:06:08)
Suggested correction: The father is her ex-boyfriend, who we never meet. This is made clear in the book, which I know doesn't necessarily count as a correction here, but we do see at the end the baby is given Fran's last name. Surely, if she thought Stu was the father, the baby would have taken his last name.