Ferdinand & Isabella Spanish Gold

First, assuming it's authentic, that's quite a find!
If you found one other example, you did better than me. I could not find another with the S between the monarchs backward.
There is also the mis-spelling ELISABED to keep in mind if looking for an obverse die match. The retrograde N seems to have been pretty common.
I think you need someone with a specialty Spain catalog. And I don't even see the Spanish auction houses trying to date these more narrowly than the regnal years.
Since the font style on this type varies from mostly gothic to fairly modern, I'd expect yours is later rather than earlier (gothic A and M remains whereas the Es and Ns are modern), but I'm not familiar with the scholarship on this.