Namewise

Started together, ended far apart

Within ten places of each other at the start of their shared record, and more than two hundred apart by the end.

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.