From what I can gather, most rotors are aftermarket, and they are all different, they all have some variance. Some fit the AM wheels just fine, some do not. I have parts store rotors and they needed a tiny bit taken off the register to fit, and a notch at the hub. I tried two different manufacturers of wheels and the factory wheels (I own a 2013 Mustang GT), neither fir without modification. It's a luck of the draw with aftermarket rotors, I hear 12" rotors clear just fine.
