It's just a name -- who cares.
Even today family names are made up for no particular reason, and have potential staying power.
Who cares whether history dictates whether Shanoa was a common or exisiting name. You weren't there personally in the 19th century, how can you say for sure such names weren't attempted?
Moreover, in a world where magic orders rise up to quell the undead armies of a reigning vampire, who the fuck cares about historic accuracy anymore?
Castlevania has only very loosley attempted to stay faithful to the eras it takes place in. It goes through the motions but thankfully it has enough balls to do its own thing with the material. That underlying quirk is partly its charm.
It's just a name. Maybe you should be complaining about ice cream cones and ramen noodles breaking the time barrier first
