In "Doug's Bad Trip", near the end, when the car gets stuck in the mud, Porkchop suddenly appears in the back with Doug and Judy, despite not seen riding with them the whole trip and stays with the family for the rest of the episode.
Doug spends most of his last week in Bluffington School trying to see the principal for the first time. However, in an early episode of the series "Doug gets busted" Doug meets the principal to receive his second place ribbon in the science fair. Since he had already met the principal, his fascination with seeing the principal for the first time doesn't make sense.