The data is stored on a metalic layer under the label but not on the bottom bottom. There's that layer of acryllic in between you and the data pits. Thus, if you grind down enough of that acryllic layer you can get the scratches out and see the data again.
Pretty well designed media IMO.
Unfortunately, after several hundred times of polishing cd's on a disk doctor and stuffing them into a 52X cdrom... they can explosively disassemble themselves. That's experience talking.