Other mistake: The interior of the house (excluding the first season), has a door from the kitchen leading outside not far from the front door on the same side of the house and no windows facing that direction, but from the exterior of the house always shown, there is no 2nd door by the front door. Instead, a large window is shown where the kitchen door should be.
Other mistake: The outside of the house does not match the interior setting at all.
Other mistake: June Lockhart is referred to verbally as 'The Honourable Judge McKay', but the end credits say 'Judge MacBride'.
Other mistake: The background action in the opening credits is slightly unsynchronized. This is most obvious at the "Goodbye gray sky, hello blue" line in the theme song, as Potsie mouths the lyrics. It's also obvious at the "My cycle hums" line, as the girl in the blue plaid skirt shows up at "cycle", rather than "my." (01:13:10)
Answer: He was written off the series, never to be mentioned again as if he never existed. As a matter of fact, according to the final episode, he never did exist.
Rlvlk