I have my own notions of what constitutes TN rifle key features, but they are not tied to dates.
As far as guards go, they simply have to fit around double triggers. The "Bean-type" is more squared off, and obviously is inspired by that family.
Deep crescent is simply a must for a TN rifle in my mind. It is a beauty mark to my eye. Perhaps I've overlooked some "flatbutt" originals, but I don't think so. I would never call a flat butted rifle a TN style rifle, no matter how much other parts/pieces and architecture fit.
The very only exception to this I'll make is for a barn-gun where the depth of the crescent must be less in order to preserve the toe. And very few of those survived. Iron was plentiful.
I'll gladly bow to original examples to the contrary. One rule in TN rifles is never say never, because exceptions did happen-but make a poor rule of thumb. If you're following a historic example, fine. Otherwise I like to fit a "pattern" and there are variations in those characteristics, but not so many.