Is there any difference between the stock hubs on these two model years?

I have a 1971 1800E that I stripped for parts when the body was too far gone. I removed the front hubs and slid them right onto the stock spindles on my 1967 122S wagon. These were the pressed-together one-piece front disks.

I recently bought a pair of 1970 1800 hubs for my sedan so that I could give it the full brake a wheel upgrade.

These hubs were a two-part style where the rotor is held to the spindle with a couple screws and the wheel itself. That in and of itself is weird, but the troubling part is that these new hubs will NOT fit onto the 1971 1800E spindles that I saved.

I've very confused, I've never heard of any differences between the front rotors and spindles on the 1970 1800 and the 1971 1800.

Does anyone have any insights??