Staub is not in the SIM because he didn't accumulate 50 AB in 1985. A player needs a minimum of 50 AB to be in the database. (Note that this is never prorated, except for 2020; 50 AB is always the absolute minimum requirement). Also note that it's 50 AB, not PA.
Once a player reaches 50 AB, he will be in the database, and he will have a rating at EVERY position he actually played that season.