Let me clarify , the vin number is stamped into the frame rail on the drivers side , it’s very easy to find by leaning over the fender into the engine compartment and cleaning the top rail !
secind cadillac used a plastic tag that was screwed on with 2 screws just under the door stricken in the drivers door jamb . It was not metal it was plastic and it had the vin number also and a place to write the mileage during service . If you have some other type of tag post a photo and I can tell you if it’s from the factory or somebody added it on