Does anyone have any tips for dating old locks?

I run into quite a lot of them, repairing and making keys, etc. and most are over 150 years old, with church wards in the better houses and, well, churches.

The last ones I worked on, we dated to between 1820 and 1837 from the Royal Warrant, but they did look somewhat older than that to me. I can put up some photos if I can get Tapatalk to work. (Does anyone else have issues?)

I've seen plenty of locks with hand cut screws, which I take to date from pre-1800 usually, since pins, nails and threaded items were among the first to be mechanised. Firm dates would be good though!