As Mike says...
A lock that corresponded to the date would probably have rounded surfaces.
The subject is simplified in that for 20 years, from 1774 to 1794 the shipment of guns and gun parts to America was embargoed by the Privy Council so there were virtually no imports from England during those years.
The locks changed over time...for example, earlier locks have a pointed tail and the 1820s they have a rounded tail. There are all sorts of subtle changes in their appearance but none of these happened all at once. Add to that the strong likelihood that older locks remaining in the inventory of some American hardware dealer could easily have been used 20 yeas after they had been made. I do think it's likely that percussion locks were the norm after 1825. I've a friend that has done extensive research into advertisements for percussion caps and it's amazing how fast the new system overtook the old. Flintlocks persisted in the military and on the western frontier where the supply of caps was always precarious but for general use in the east I doubt many were made after 1825. I'm also certain many unused flintlocks were converted to percussion when assembled into a gun...after all, all the gun maker had to do was remove some parts and fit a new cock. On American guns the percussion cock hits the nipple. On best quality English guns it actually stops a few thousandths short of the nipple...just close enough to detonate the cap. Fitting percussion hammers became a specialist trade in itself.
It looks as if Liege took over the bulk of the export lock business in the percussion era based entirely on price. Belgian guns and parts were even cheaper than the Birmingham products and with the end of the Napoleonic Wars, as well as the restrictions of the Navigation Acts, it was practical for Americans to import them from the cheapest source. There are numerous "fake" Ketland locks, and guns, made in Belgium that arrived after 1816.
So...you have an English-made lock of the late flint period. As Mike has said, the lock on that 1769 fowler is of a style very common from 1795 on...but not earlier because that style was not being exported earlier.
I should also add that the Ketland's were by no means the only exporter although they appear to have been the largest. When the Privy Council relaxed the embargo in 1794 the floodgates opened to take advantage of the American market. As far as marked/unmarked is concerned...ALL the export locks were made by specialist gun lock makers. They would make them for anyone that could pay for them.