Board Thread:General Discussion/@comment-32742667-20170801135452/@comment-1038387-20170802103642

The problem is, it's not "would have known", it's "could maybe have known".

There was one Ring, and numerous lesser rings. They were not created with specific recipients in mind, though their powers suggest they were created in that number for each race.
 * Celebrimbor kept three. Two were given to Gil-Galad, one to Galadriel.
 * 7 went to "Dwarf-lords". It's usually interpreted as the heads of all the seven Houses, but that is never made explicit. One was a heirloom worn by the head of Durin's Folk.
 * 9 were given out to "Men", no specification given. Unlike the Dwarves, there is no clear connection between the number of rings and the number of houses/kingdoms/lands that warrants speculation. One was an Easterling. Don't know the rest.

There's no reason to assume Elrond would know every Mannish lord or champion across the world, or even just the nine who got the rings. Especially since they were busy hiding their own realms from Sauron at the time.

And as the Nine faded, their former names became irrelevant to everyone, even themselves.