Even with my untrained eye that this coin have some cleaning performed by the original finder. 😩
I can understand the effects of corrosion as in this excerpt discussed among Ben's colleges...

…As I understand the problem of low density applied to silver coins salvaged from sea water wrecks, the problem should always be anticipated to some degree. Electrolysis of reactive metals in sea water is commonplace and a silver copper alloy can itself act like both the anode and cathode in the reaction. The silver being less reactive is not removed in this way but the copper is. This means that microscopic copper grains that form in the alloy when it is cooled will leach out of the alloy starting at the surface first. The longer the item remains in sea water the deeper the effect will go. Hundreds of years in salt water can result in leaching that permeates deeply into the coin. This does depend on a number of factors in the environment – temperature, salinity and the presence of other elements.
The result of such corrosion often is a coin which yields a higher silver and lower copper content when testing using XRF. XRF is only a surface reading but it is indicative of the loss of copper…

My coin specimen is 25.85g compared to the original 27.2g so there is a marked loss in weight. I also have two coins from the El Cazador ship wreck and the leaching traits have some similarities.
The discussion also mentions comparability with coins from the El Cazador too.

I appreciate the comment @emaxisonline 👍