I doubt that the plate on the rear door was ever for a wheel carrier, it is too low to mount a wheel, and would have covered the tow hitch, and most likely dragged the tyre on the ground on the slightest of humps in the road, let alone how it would have caught on crossing driveways.
here is a picture of my rear door, oh, and this is a station wagon, the station wagons had rear sliding windows.
This picture was taken on the day I bought the car.

