The worst is when an insert set is 10 cards. 1 full page and then 1 left over card.
In 1990 Upper Deck introduced the baseball card collecting world to it's Baseball Heroes set, which would continue over a couple different product lines from 1990 - 1997. They would resurrect the Baseball Heroes concept in 2002, but that was different.
Starting in 1990 with Reggie Jackson being cards #1 - #9, the set continues through 1997 ending at card #100.
The problem with the 9 card set is that there is also a not numbered header card, a 10th card.
But wait, the back of the Header Card even says that it's a 9 card set.
Here's the 9 cards.