yep i'm with you there, but what i'm saying is that once you stick on the new rotor, you don't need to worry about the old rotor centreline - only need worry about the replacement rotor annulus (at a zero offset) for geometric fit...
ie the face that bolts onto the hat is flat, and as long as the bolt centres are right, and the thickness is right, then the rotor centre should be in line with the bracking work...
hmm do i make any sense??