For cars/engines in years that did not get the engine VIN stamp, it's much easier to find a GM original engine that is 'A' correct engine for your car. Even though it's not 'THE' born-with engine, without the VIN, it's impossible to prove that the engine didn't get installed in that car (assuming the date is within an allowable range, and all the associated parts/work match up correctly. In such a case, there is no reason to modify any of the markings on the engine to be 'correct' for judging.