Year - 1991
Main Brands - Topps, Donruss, Fleer, Score, Upper Deck
Number of Players Included Among All the Sets: 37
Players Included in Every Set: 20
It's the same five again. In fact, it will be these same five for a few more years. Bowman, Stadium Club, Leaf, and Ultra among others are all on the scene by 1991, but I'm just doing each company's flagship brand.
The yellow borders on the Fleer cards make them pretty easy to find!