Things that don't happen on this show
Unless I missed an episode or can't remember a subplot or two--
I don't think we ever saw any of the Owens' relatives. No cousins or grandparents. Hard to believe George and Marsha would have both been an only child and that all four grandparents would be deceased. I suppose if the show had run longer, we might eventually have seen some relatives visiting. Not only do they not visit, I can't ever recall any of the Owens' extended family being mentioned in passing or being spoken to on the phone one-way.
We never learn what the Owens are paying Belvedere. Jokes are made that George is usually late with Belvedere's check and Belvedere complains it is a paltry sum to begin with, but the actual amount is never specified. Is it?
We never see the Owens basement. It is referred to several times. In the one where Belvedere goes to work for the queen, Wesley is shown having a casino night down in the basement, all off-camera. And in season 6's 'Love Fest,' Marsha confides to Belvedere that she and George were trying to reignite the spark in their love life by playing Tarzan in the basement.
We see Wesley in a grade school classroom, and we see Kevin in a college class, but we never see Heather in the classroom. There is an episode where she and Angela are trying out for the debating team but we can assume that is after school hours in a multi-purpose room.
Not sure if it is properly explained how Robert Goulet knows Belvedere and the family. Unless I didn't catch the explanation in his first episode as a guest star.