Are e12, e24 brake rotors manufactured to be able to see any seams in the vent ribs ? Rectangular holes between the pad surfaces, those ribs.
A friend had a '90's Dodge Van front rotor separate. Not coated, ours always show rust in the vanes from the first month of driving in the rain.
Looking closely at the front rotors of my '81, I can see what appear to be seams in the center of some of the ribs. Not what I would call cracks, but not looking solid as if a perfect one piece casting,...blah blah.
I thought rotors were only about minimum thickness until I heard the friends adventure story.