I recently acquired a used CD. Not that you could tell by the look of it though, it was perfectly spotless. I looked closely at the layer of recording material and it was perfect. Then after I played the CD for the first time, I looked at it again. It looked different. You cloud see the leftover area on the outer edge of the layer where nothing had been recorded. Which is nothing new, but why the change from being perfect to having this change in appearance? What happened here?