16th century metal just has a different look than 19th or 20th C metal, in this picture you can see the difference on the surface of the helmet.
The black spots are not from damage but older metal has more impurities that over time translates in the more visible cracks , black spots and as here delamination.
None of these traces look homogeneous or uniform on 16th or 17th C metal, there is nothing repetitive about them.
In Attempt to mimic these signs of age they use various methods, for instance damages, or chemicals to create rust, the results exits in as many forms, but none have the exact look of the originals.
Once you master to recognize this difference you can start identifying the reproductions.
I suggest you read scams and fakes a lot is explained there
http://www.vikingsword.com/vb/showth...ighlight=scams
IM afraid its not exaggerated, and as Michael pointed out the current scientific dating method is accurate by a 500 years margin.
kind regards
Ulfberth