Alternative Explanation

Elves are usually described as long-lived, but what if they just all look the same so nobody can tell? And they have a small pool of names. You could get away with a bunch before regular censuses.

Addendum

I presume we'll already have magic by then. If not, we should start with dwarves.

Grim but Inevitable Future Conflict

When genetic modification techniques have advanced to the point where we can make elves, how will we decide what interpretation to use? Decades of internecine war, of course. I'll be rooting for tall, but outside of that I can be flexible, even collaborative.