Michael, the date stamp you mention that is 12/71 Dec 71.
In my experience in industry its far more common to use WEEK/YEAR nomenclature rather than MONTH/YEAR. I would imagine Rover were producing hundreds of cars a week / thousands of cars a month. Suppliers would have been delivering parts on a daily/weekly basis. I don't think MONTH/YEAR would have been much use to them as a way of tying down parts to a particular batch or delivery.
In my experience in industry its far more common to use WEEK/YEAR nomenclature rather than MONTH/YEAR. I would imagine Rover were producing hundreds of cars a week / thousands of cars a month. Suppliers would have been delivering parts on a daily/weekly basis. I don't think MONTH/YEAR would have been much use to them as a way of tying down parts to a particular batch or delivery.