The "Laser cut" theory is bull. It'll take way too much time to do that for every chip. There's probably a few NAND flash cells built into the chip, preprogrammed from the factory that cannot be access through regular means which control which parts are disabled.

All you've done is make the drivers and VGA bios think that the chip has extra shaders which are still disabled so when it tries to initialize or access them, it screws up. The artifacting on desktop is more likely a memory issue.