sorting out the difference between a 1755 knife and a 1780 knife is difficult
1755 vs 1780 is a tough nut to crack with many forms unless marked (Sheffield directory starts in 1774 as far as I know)...I'm not sure of a really good big book of pocket knives that is comprehensive for 18th century folders. The first really good "catalog" images that I know of are 19th century for English stuff. There are a range of them in the typical forms shown above and some really odd pen/fruit knives, seal knives, mohock knives, multi tool knives and etc. One could certainly go off of the Sheffield maker's marks and xref that with dug items for date bracketing.
a lot of everyday items In the 1750-1850 time period did not change much or a all
for some things yes, however folding knives don't seem to be one of them (a few pen and specialty forms aside).
The folding knives off of the Arabia from 1856 are WAY different than the mid 18th to early federal era knives, but there is some fuzzy cross over from say 1770 to 1800.
I will say with the bigger non pen/fruit knives you generally don't see nail nicks until the 19th century (although they are certainly around on smaller knives with less blade area to open way earlier)
Smith 1816Fisherman's knife off of the Arabia ca. 1856This pocket knife recovered from the Arabia has a very interesting maker’s mark. An image of a fish with the words "THE FISHERMAN'S KNIFE" is etched into the metal on the large blade. The name of the manufacturer is etched into the small blade, reading "G WOODHEAD 56 HOWARD ST SHEFFIELD" Many of the pocket knives found on the Arabia were produced in Sheffield, England.