I have an interest in building flintlock rifles. Some of the gunmakers that do this work often want a gun that looks as if it is a couple hundred years old and finished with period correct methods/materials (for legitimate purposes). Some have developed the techniques to the point it is virtually impossible to discern originals from contemporaries. Not sure even a chemical analysis would help as old metal and the finish materials are still available. I understand that the publication of high grade Parker serial numbers outed more than a couple upgraded counterfeits long believed to be factory originals.
