Wow.
Set listed here:
https://www.tradingcarddb.com/Checklist.cfm/sid/65992/1990-Star-Geneva-Cubs
Set does not include any NNO cards. Yet it does have card #26. (This is significant because we printed on 100-card sheets, and we'd set up 4 teams on one sheet - 25 cards per set. Cards 26 and up, and NNO ones like this one would be on an "orphan sheet" - one sheet to handle all the leftovers. Sometimes the orphan cards would not be ready to go in the sets to go out and would go separately (this is why some sets are listed as "25 or 27 cards" in some cases).
Sometimes cards like these would be made as a courtesy to the staff, sometimes not even intended for distribution with the set (hence the lack of number). I don't remember this card in particular, mainly because it has been 28 years. If anything, it may need to get added to the set as a single promo listing, not as part of the base set.
-- Dan --
Note: Please see my profile for more info regarding trading (section updated 3/4/2024). I have added a large portion of my inventory to the site, and currently have trading turned on (details are in my profile).