We'll need to see a few pictures of the car before commenting.
On your own you can start by inspecting the VIN plate located behind the spare wheel.
Does it have the same VIN number punched on the frame tunnel under the rear seat?
Does the VIN number on the tunnel match with the Chassis number on the reg. documents?
Is the car a German production?
Inspect the rivets that hold the VIN plate to get an idea if the VIN plate has been re-attached using blind rivets.
Another sure sign that it is a post 72 car would be the size of the rear window. (which is larger than the one on a 69 car, unless its a Mexican car which did have smaller windows even in later models)
what kind of tail lights does your car have? It should have the larger elephants foot type. Its highly unlikely but entirely possible that the rear fenders were changed. (In Pakistan you find the later fenders on early cars to give them a modern look, not the other way round)
there are more signs but lets start with the above checklist and see where we go from there.
