Yours has the same wear marks near the binding/fold. I wonder if they all do that.
Mine looked like that too...
I've noticed this in a lot of jewel case games with a decent sized manual. Here is my collectard guess/explanation:
When you stack CD games vertically on top of each other (each one laying fully flat on top of the next), the combined weight eventually pushes down more on each of them. Then when the stack is moved or anything you're essentially rubbing the manual against part of the CD tray, making the coloring on the manual wear away.
If you look at this one as an example (and I've seen a lot of PS1 games with the same kind of thing), you'll notice the rubbed away part only happens where the tray isn't cut out to hold the cd. Why does it only happen near the edge of the manual? Probably because that part with the staple is the thickest part of the manual and the first to be "rubbed raw". teehee
I'm sure turbo games show it a lot more than others due to the overall age and storage conditions. It's a lot easier to stack and carry games one on top of another. Once I started noticing this I began storing my games standing up on CD racks. I also put a thin piece of foam or bubble wrap where the tray spindle goes to avoid having it rub either, I learned about that trick after getting lots of JP games like that.
