Plot hole: The parents meet and get married on the QE II and then we jump to the girls getting to camp 11 years and nine months later. We learn their 12th birthdays are on October 11, so at the time of the camp (which must be around July/August) they are 11 years and around 9 months old. They should only be 11, given it takes 9 months to grow a baby, but instead they're nearly 12.
Suggested correction: Elizabeth James got pregnant sometime within the 11 years. Their parents sent them to camp in July because in October they both turn 12. So they are 11 years 9 months old.
The mistake is valid, but perhaps not specific enough about why. The opening scene takes place Jan 8, 1986 (as seen on the marriage licence). Then it says 11 years and 9 months later, which would mean in the next scene it's October 1997 (when it's July 1998). It's 11 years and 9 months after the twins' birth and/or the parents' divorce. But we're not actually shown that part.
Plot hole: When Annie (pretending to be Hallie) lies to Meredith about her father's "routine" with ladies, she mentions how he gives them a bottle of his "special reserve label wine." He then approaches them and really does offer the special reserve to Meredith. It's impossible that Annie was able to predict this. She expected her father to be single, based on what she was told by the real Hallie. Neither girl could guess how he behaves with girlfriends.
