Early 18th century you will see more variation, L-W.
After that, the shell in its variations was pretty well it for a long time.
a bit later, say 1775 on, we see some differences, like occasional silver wire work instead of the shell.
Often though the silver work is in the fashion of a shell!
(I still have one by Wooley C 1780 to repair which has a silver wire shell.)
One thing though, the shell on better arms was normally beautifully done, and to my mind is the height of elegance.
Best.
R.