Shakespeare used Gertrude for Hamlet's mum, the queen of Denmark, so he seems to have associated it with northern Europe.
I find some of the entries in your 1796 list fascinating: Hierom, for instance, but not Jerome. Strange! Rice I suppose is Rhys. Could Benigma be Benigna, if the printing is sometimes unclear? That would be less odd. As for Fortune, Hagar, Jacquet and Sisera ... who says the world hasn't improved?
I don't imagine the compiler of that list did original research as we would understand it: probably just liked names and noted them down when he encountered them. Nice chap!