When Emily is born, Sammy is two. About 13 episodes later, Sammy is still two, but Emily is now also two.
When Billy makes his first appearance, Jimmy introduces him to Greg. However, in Jimmy and Christine's wedding video, both Billy and Greg are in the wedding.
In the opening credits of the earlier shows, the two families are seen crossing a road headed toward a beach. As they switch cameras, Jimmy is shown behind Christine then next to her and then behind her again.