CRITICAL BUG - Error When Adding Missing Cards To Sets

There are a few different cards from multiple sets I can't add to missing cards. I receive an error saying that the set is complete and therefore I cannot add any cards, yet this is a mistake. Your database is counting incomplete sets as complete and not allowing me to add cards to finish sets.

To assist, here are a few card details with this error.

NBA - 1993 Topps Black Gold - Winner A [Redeem Card] #Group A
NBA - 1991 Front Row - Dikembe Mutumbo #16
NBA - 1999 Skybox EX Tracy Mcgrady #17

Edit: I forgot to mention, to my knowledge there is no way to add a missing set to your database. For instance, 1974 Fleer Cloth Stickers

(I emailed this to webmaster address as well as this is a critical bug IMHO)