I think what we learn from these investigations is that there was a wide assortment of variations in firearms that weren't standard factory and there were some very good 'forgers' who made things look factory. I have a D grade Parker that left the factory with a pistol grip. I bought it with a straight grip and a long trigger guard with proper serial number stamping and engraving. My stocker who is refinishing it says the stock is not original. Where did the trigger guard come from? Go figure.

Nothing is foolproof to a sufficiently talented fool.