Most people date a lamp by the shade or the base. Joe dates it by the socket. Pull the shell off a pre-1930s fixture and you'll usually find a paper liner, a friction-fit shell, and a two-piece cap that most modern hands haven't touched in decades. Push-through turn knobs came later; pull chains later still; the keyless socket outlived nearly all of them because it was the cheapest thing a fixture manufacturer could ship.

None of that is a hard rule — parts got mixed, repaired, and swapped for a century before anyone thought to keep records — but the socket is where the honest evidence usually lives. It's also the first thing that gets replaced when a fixture is rewired badly, which is its own kind of tell.

Every piece that leaves the bench here gets a new socket rated for current use, but the old one doesn't get thrown out. If it's original to the fixture and still readable, it goes back in the box with the piece. What's original is called original. What's new is called new.