WRT gaming the system, most seem to include a convention to hide the mark, and often it only appears at puberty. But yeah, you'd think unique names would be a lot more the norm. I mean I think the system of last names at least would have developed differently, so that duplicates would be less common, and people found more easily. Like even just a typical last name not being say "Baker" (because some ancestor was a baker) but "Baker of village such and such" would help a lot for people to track down their soulmate's family.