Most visitors online was 1660 , on 12 Dec 2020
I don't know about it only being applicable to the "earliest" movements. I have a nickle 6s Elgin from around 1895 that has the full compliment of serial numbers on almost everything, including the barrel cap.This makes me curious about the earliest movements, where the serial numbers were stamped on even parts as generic as the barrel and barrel cap. I presume that early manufacturing processes still required a lot of hand fitting of parts for best function, so I wonder whether all the parts that got serials were stamped before assembly? Or after test fitting?