The coin could have been a re-strike from an old die. I do not know the 
history of Spanish coinage, but this practice was done by several European nations 
for legal reasons. In fact, after the United States outlawed hoarding gold in 
1933 (but allowed antique coins), European mints used old dies to restrike 
coins to be legally sold in America. 

Then there is the issue of shipping obsolete and old coinage to the Americas 
simply because this place was currency poor. Some people believe this is how 
Viking and Roman coins ended up being traded to Native American settlements in 
the 17th and 18th centuries. Until local coinage became the custom, all sorts 
of odd coinage could be used in trade and exchange. This is why the British 
developed trade dollars for their dealings world wide. As recently as the 1970s, 
locals in Burma were still using mid 19th century British trade dollars in 
remote mountain camps. 

Ron May
Legacy 106, Inc.