1991 Upper Deck Baseball
There should be some kind of method to add missing cards to sets already marked as "complete". For instance, 1991 upper deck baseball is missing card numbers 44, 45, 46, 48, 78, 80, 81, 94 and 96 out of only the first 100 cards.
We have all of those cards. It looks like you might have "Exclude variants" turned on. Those cards are flagged as variants because of their name (which I am going to fix). If you ever see cards missing that you expect to be there, please remove that exclusion and see if the cards do show up.
https://www.sportscardspro.com/game/baseball-cards-1991-upper-deck/kelly-gruber-blue-jays-checklist-44