Addison tells Callie that 8 months ago she peed on a stick and was pregnant with Mark's baby. This wouldn't be possible, as earlier in the season, Mark said to Derek that he must feel he wasted a year of his life trying to make it work with Addison, when he and Meredith could have really had a shot.
Meredith refers to the baby Montgomery & Karev are caring for as "Laura Grey" but the child's name is actually Laura Thompson. The baby's mother's maiden name is Grey, but she is married.