Depending on the vehicle some places dont turn rotors anymore they just replace them. They just don't want to be liable for any potential failure. For instance my wife has a 01 330ci and when her brakes went bad manufacturer specs said that the pads, rotors, and abs sensors had to be all replaced. Front and rear had to be changed out and the parts were over $500. Its ridiculus but it was the "safer" solution. Originally I just wanted to replace the pads but it is my wife's car and I didn't want to take any chances. As far as the discard specs, its usually found on the inside of the rotor that faces the hub so you will have to pull of the rotor to see it. If you have access to a manufacturers database or some other program like Alldata or Mitchells On Demand then you can find it there too.