Gus you are correct about a too broad generalization, and blending of time periods. This what happens when an exhausted night shifter posts while still having only his 1st cup off coffee upon getting up from a post work nap. Lol.
I still think, given that there were often apprentices involved, if not a few workers with specific tasks, to free up the master builder/smith, that some at least minor embellishments would have been common. Maybe tang border carving and something simple behind the cheek piece, or something incised lines down the forstock, would have been more common than all this beautiful curly wood we see now?
Also, if we put carving and engraving aside, some "poorboy" or "barn gun" features don't make sense to me.
If I'm buying all the gun I can afford, and will be relying on it to feed and protect myself, I need that gun built to last. I'm certainly not going to risk splitting the stock by not having a butt plate. Even if it is used off a musket or broken fowling piece, "please Mr. Builder, put something there to protect my gun."