Long story short, it had long been urban legend that Atari buried thousands of copies of ET for the Atari 2600 after the game flopped. It's considered by many to be possibly the worst console game...ever.
Having had it myself, I can verify it was indeed awful. Worst ever? Not sure about that.
I wonder if they'll find any of the Swordquest games too?
Yeah, but that's the point -- the add-on was redesigned into a stand-alone console, and the new _stand-alone_ was the system that succeeded. It's not as if Sony said: 1. Our CD-ROM add-on for the SNES was rejected. 2. We'll release it ourselves. 3. ?...