They call it "calibration" when it's presumably nothing more than writing a serial number to an EEPROM somewhere. See also the related story of sabotaging iPad screens to work but subtly degrade when the serials don't match, and cameras that only semi-work when swapped (with genuine original Apple parts). This type of pathological lying that Apple loves to do is why I'll never buy or recommend to others any of their products.
https://news.ycombinator.com/item?id=24955071
https://news.ycombinator.com/item?id=36926276