I'm not surprised there was a switch. This seems to be continuous across the industry. It is a 65-67 Mustang front rotor and has been one piece with the hub for four or five years WITHOUT a part number change or even a notation. Been there, done that.
Considering that fact, personally I am in the group that says if "we" are going to screw around with making a rotor for the rear, make it vented and so it mounts over the wheel hub so it is simple to remove to have resurfaced without tearing the rear assemblies apart.