Such was the case with a new blank space for a 1986 Sports Illustrated Poster Test Sticker #4286, that showed up recently.
The problem for single player collector's, is that once your collection is past the beginning stages, it's fairly easy to buy a card you already own. The Sports Illustrated sticker sounded familiar and a quick check of ebay showed the Herschel card in question, albeit graded, and for a pricey $200.
I decided to pull out my original Herschel card binder, and go through it again. I have the cards in chronological order, for the most part, but some odd shaped, and over sized cards are in the back.
Lo and behold, I came across the test sticker in question, already in my possession.
The back of the card is blank. Now I doubt that I'd pony up $200 for this card, graded or not, but the message is, when you see a potential need for your collection, take a minute and make sure you're not buying something you don't already own.
I should note that many collectors don't mind, and actually seek out duplicates, but I have enough trouble trying to keep my one of's straight.