I'm glad I could help. :)
Do you have a reference to the fact of
Emlyn being a place name only used as a given name in Wales after 1800? References such as Withycombe or Hanks, Hardcastle, and Hodges don't mention a place, but only the theories that it could come from Latin Aemilianus, or perhaps from an Old Celtic name which was "Latinized" as Aemilianus.
I do notice that
Welsh Personal Names by Heini
Gruffudd does mention a place, Newcastle
Emlyn, in Dyfed, Wales, but it also says "could be from Aemilianus".
As an American, these entries seemed to imply
Emlyn was in use before 1800, but I certainly assume that as a European closer to continental references that you are probably right and it's just one of many "Welsh" names introduced in the 19th century. :)