Eureka! You seem so convinced that something impossible was true. So I called one friend and a few dealers, the most knowledgeable is out of the country and didn't respond. So I thought maybe the thing to do was search for info on Google in Spanish, which is not my first language, nor second third or fourth.
But I can read it somewhat. Anyway I found this site pdf file.
http://www.ascasonline.org/gonzales.pdf
I contribute to the site, and they often have translations, but evidently not in this case.
The gist of it is the author does not believe the marks shown (unfortunately not really clear) are those of Diego Gonzalez but that of Nicholas Gonzalez de la Cueva who was assayer between 1701 and 1713.
So unless someone comes up with a better explanation, the Boylan book was wrong. And evidently your dating of the wreck was accurate.
Maurice