Accidental Autographs: How does this even happen?

Yesterday, my friend and I weathered the impending thunderstorm and went out for one of our regular coffee and cupcake outings. She had been telling me that a book that I had recently checked out of the library, read, and loved (specifically, Clockwork Angel) had been spotted at Books-A-Million for the clearance price of $6.97. How could I resist? We decided to make a quick stop and, sure enough, there were three copies left. I found the copy that I thought was in the best shape and happily bought it, along with one more book that I couldn't turn down. Here is where things get surprising. Later that evening, I sat down before bed to admire my new clearance finds. As I carefully peeled off the clearance price sticker, I noticed a small gold sticker a lot like this:

(image found here, at Waxcreative Design)




My response? I'll admit it: I gasped, "squeeeed," and danced around. Then, I second-guessed. Surely this must be some mistake. Why would BAM put an autographed book on clearance? I had never seen such a thing before. No, I'd just check inside to see if there was actually a signature. I found this:

I thought I was going to keel over right then and there. How? Why? If this one is autographed, what does that mean about the remaining two books still sitting on the shelf? I texted my friend (who is a big Cassandra Clare fan) and shared the surprise. Her response was, of course, "What?!?!?" I couldn't have said it better, myself