Many locks have long production histories but also have clues to help date them. A nice article on Miller push-key locks was in the West Coast Lock Collectors' newsletter, April 1998 page 5, by Bill Cunningham. He states that Miller started using a scroll trademark which was registered on October 9, 1906.

I can't find this registration at uspto.gov, even doing a search for all registrations on that date (only 9 of them), or searching for "Miller Lock Company". So I'm wondering where Bill got his information, or if I am really that bad at searching for trademarks!

He also asserts "Of course, locks marked with this scroll trademark were made after October 9, 1906" but I would disagree, it's possible they used the trademark long before they bothered to register it. That's why I would like to find the trademark registration, it usually includes a (claimed) "first use" date.

Jim