I do not belive this is accurate. From the set notes, "Distributed in a cello pack at the 1995 National Sports Collectors Convention in St. Louis. Cards have the same appearance as the regular issue cards but are unnumbered."
Here is an example of the Vin Baker card,
Promo:
Base:
That is, the cards would have printing on the back, minus the card number in top right. If there is no printing on the back as Jedwabny has stated, then it is likely a printing error.
https://www.tcdb.com/FAQ.cfm?ITEM=PrintingErrors
https://www.tcdb.com/FAQ.cfm?ITEM=Pricing#6