1991 Upper Deck is an 800-card set released in two series: A "Low" series of 700 cards, and a "Hi" series of 100
Look for the following inserts in Low series
Nolan Ryan Baseball Heroes
Heroes of Baseball
Nolan Ryan Autograph
Heroes of Baseball Autographs
Randomly inserted into Lo (SP1) Series packs is a limited edition short-printed, or "SP," insert. SP1 shows Michael Jordan taking batting practice before a 1990 White Sox game.