Trying to attach a video progression with an 1843 N4 large cent but don't know what format is accepted here. This is a screen shot; image lines up nearly perfectly!
I wonder if there's another one out there with an overstrike. Have you seen other 1796 S-85 struck fakes? I dug this up from a 1913 Numismatist article that indicates over 700 old dies were destroyed in the 1860s. If these 1796 cent dies were still around it sounds like they would have been destroyed then. I'm just thinking about the "mint sport" idea and when that could have occurred.
I starting thinking counterfeit when I saw the toning. The Chinese copper coin counterfeits have a look to them that seems to be pretty consistent. Of course that is not a good way to say that the piece is bad, but it should set off some alarm bells when you see that type of toning. As for the comment about "old corrosion," of course the thing has old corrosion because it was made on a cull large cent planchet that was corroded. The half a century difference between the date on the thing and the date of the large would not make a difference.
Jack Is (or could) this coin be "oiled"? https://www.cointalk.com/threads/mineral-oil-on-old-copper.392736/#post-8198956
I'm talking about the corrosion right up against the letters and bottom of the bust when you zoom the initial images provided. It doesn't look like remnants of corrosion from the original coin to me.
I think you are on the right track - just not Sure it is an 1843 N-4 under type. I can't get the tips of the star to line up. I think my overlay does highlight the "TY" in "LIBERTY" of the under type.
I agree @justafarmer , we continue to refine the variety; the reverse is probably a small letter reverse instead as well, as we continue to work that out. But we are on the right track with petite heads!
@justafarmer Just to add. Your overlays are always a big help and add to the research on subjects like this. The assistance is appreciated by others that are using this as a learning opportunity