Regional architecture leaves its mark on the smallest parts, so a house fitting often carries a place as well as a date. American building never moved evenly across the country; climate, local materials, immigrant trades, and the years when a region grew all shaped what got built and what got hung on the walls.
Climate did a lot of it. New England houses, built against hard winters, ran to tight construction, storm windows, and the hardware of a battened-down house. Southern houses opened up instead, tall windows, transoms, porches, the fittings of a place trying to move air rather than trap heat. A window's hardware, sash weights and locks versus louver and transom mechanisms, often tells you which climate the house was answering.
Timing shaped it too. A region that boomed in the 1880s filled with Victorian building stock and Victorian parts; one that boomed in the 1920s runs to bungalows and Deco; one that grew after the war is mid-century through and through. California, growing fastest in the twentieth century, is heavy on Craftsman, Spanish Revival, and mid-century fittings and light on the early Victorian hardware that fills older Eastern cities.
None of this is a strict rule, since catalogs standardized much of the country and material travels, but the tendencies are real, and they're part of why an experienced eye can often place a fixture geographically as well as historically. For a buyer matching a specific house, region is worth keeping in mind. A part that suits a New England colonial may look wrong in a California bungalow, even if both are antique brass.