Anyone can fake a shade tag; almost nobody bothers to fake a socket. That is why the wiring path — cord, switch, socket — is the most honest dating evidence on an electric lamp, and why collectors check it before they read the label. The parts changed on a predictable schedule, and a lamp whose parts disagree with its style is telling you it has been repaired, married, or built from parts. Here is the schedule.
Early electric sockets (roughly the 1890s through the 1910s) used a push-through socket — the entire interior cartridge rocks or pushes to make contact — often brass, sometimes with a fabric-insulated interior. The turn-knob socket, where a small knob rotates the lamp on and off, becomes standard through the 1920s and 1930s and never really leaves. The three-way socket (low-med-high-off in sequence) arrives in the mid-1930s and signals a lamp made or substantially updated after that point. Pull-chain sockets show up across all eras but dominate utility lamps, not fine table lamps.
A caveat that separates beginners from collectors: sockets are the one part that gets replaced as routine maintenance. A 1910 lamp with a 1950 socket is not fake — it is serviced. The socket gives you a "no earlier than" date, and the rest of the lamp has to agree with the rest of the evidence.
The cord is the best quick-read on the list. Cloth-braided cord over rubber insulation, with no ground pin, points to pre-1940. Early plastics — bakelite and similar early synthetics on plugs and switches — belong to the 1930s and 1940s. Modern PVC cords with molded plugs and a polarized or grounding plug say post-1960s at best, and usually say "re-wired within living memory."
Untangle two signals: original cloth wiring makes a lamp more valuable and less safe. Collectors photograph it, document it, and still rewire for daily use — keeping the old cord in a bag with the lamp. Wiring you replace is not value you destroy, provided you keep the original and tell the next owner.
The inline switch on the cord moved through its own eras: rotary and push buttons in brass or bakelite through the 1930s, larger bakelite sliders mid-century, and small molded plastic rockers late century. A brass turn-knob socket with a plastic rocker in-line switch is a lamp that was serviced, not a lamp that was born confused. On fine lamps, check whether the switch is built into the base — integral base switches are a feature of higher-grade lamps and were done carefully; a visibly added hole in the base for a retrofit switch is value damage worth knowing before you buy.
The routine, in order: read the socket (no earlier than), read the cord and plug (last serviced when), read the switch (servicing quality), then check whether the base, shade holder, and harp agree with each other. A lamp that tells one story end to end is "original condition" or "sympathetically serviced" — both good. A lamp whose parts argue is a parts marriage, and the price should reflect it.
For precision, pair this with the maker's mark hunt on the base plate and the metal test on the column — the three checks together date most lamps to within a decade without an appraiser.
Half the questions that reach a lamp parts counter are dating questions wearing a repair costume: which socket fits, whether the old cord can stay, what a three-way upgrade means for a 1920s base. The answer always starts the same way — date the parts you have first, then decide what the replacement should be. A directory full of lamp parts and categories is only useful once you know which decade your lamp thinks it is living in.