good thing the rotrs are drilled/slotted. if they were plain rotors, you would'a had a problem putting the old pads on. the pads will not be 100% flat from the old warped rotors. all rotors get warped after a few thousand miles, its innevitable. the old pads also become warped from the rotors. so putting the old pads on the new rotors would warp the new rotors faster to more severely. however, you have the slotted rotors, which act like a razor blade and cut a small amount of the surface of the pads with every rotation. the slots in the rotors will clean up the pad for you, but i personally would never do that to my own vehicle. i would to a customer, but not mine.