I have seen very elaborate engraving as you note, but have also seen virtually "none".
Here is a close up of the lock on a very nice Manton Half-Stock (2 keys, checkered wrist).
There isn't much more than a (border) engraved around the perimeter of the lock plate and a little on the hammer.
I am just getting into engraving and still doing a poor job (need lot's more practice), but certainly something of this style I would consider within my abilities, with a lot of patience.
Anyhow, here's the pic -