What does one who is new to 1873 springfields need to look for when examining supposedly "correct" pre-1876 rifles? Any "bannerman" things to look for?

Lock plate differences?
Breech block markings?

I know about the thin wrist and the later type stocks, different sights, etc. But am not sure about the actual markings on the parts above, as I have heard that the markings changed during the production run.
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