A Spanish/Guatemala 8R 1820 - Contemporary Counterfeit?

Hello all friends,

I show you two coins of same type and same year, one that I think is real and the other is a counterfeit but I don't know whether it is a modern forgery or a contemporary counterfeit.

In fact, I can't find too many difference from both coins because there seems no difference in size, thickness, diameter, striking characteristics and also the edge patterns(circles and squares in nearly same phase) of both coins. The only difference that I am sure is the difference in lustre of the two coins. The real one is naturally toned and the one I think fake does not look like silver-made. I do the S.G. of both coins today for confirmation.

The one I think real is at the left and the one on above of the edge pictures.

Specifications:

"Real" : 26.61 grams, 38.3-38.5mm, S.G. 10.185, US$90.0 (bought two weeks ago on ebay), two edge overlaps clearly seen.

"Counterfeit" 26.8 grams 38.1-38.3 mm, S.G. 9.65, US99.0 (bought about 2-3 yrs ago), two edge overlaps clearly seen.
This is the 3rd time I do the S.G. of this coin, the last two times were 9.73 and 9.63. So I am quite sure this "counterfeit" coin is low in silver fineness. The ring test also suggests both coins are of different silver content.

The Riddell book had never shown this coin as an example of counterfeit.

Can anyone give me some idea whether it is a modern forgery or not? It is also good to show the same coin if you have.