Larry states that both Stephanie and Darryl have AB- blood and thus Stephanie has Darryl's blood. While it's true that AB- is the rarest blood type, it is not true that a blood type must be a perfect match except in the case of a recipient with O- blood. Stephanie could have received blood from any type as long as it was Rh-. It would have been more accurate to say that they both had O- blood.