Namewise

Mirrored each other

One rose by roughly as much as the other fell, over the same twenty or more shared years in one published list.

1200 pairs, drawn from the 2,573 names with a recorded popularity standing (common, familiar, uncommon). Every one comes from a single published list, where both names were measured on the same scale, in the same year, by the same registrar — so each is a fact about that ranking rather than a similarity judgement, and never a claim that one name displaced the other.