Even more interesting is the uncovering of the "B"-numbered engine information contained in the dealer account books.
Previous literature has mentioned the fact that Ford made 12,247 B-numbered engines "during fiscal 1913 in Detroit." Apparently these engines were built in the late summer and early fall of calendar 1912 and seemed to have gone into the bulk of the cars assembled between October January 1913 (1913 models).
A representative sample of each lot of weapons is tested with a proofing cartridge, which has vastly higher pressure than the normal specifications.
If the weapon survives a certain number of these, it passes, and all weapons in the lot get the proof mark to certify they meet the government's minimum expectations of function and safety.
This practice became most organized, and earned the name of "proofing" with the advent of firearms, when armor plates were proof tested to assure their resistance to (proof against) early gunfire.