Richard, its really good to have you come in on our discussion!!! and I was hoping you would but hadnt seen you posting for a while. Welcome back, and thank you for the as always, great notes. You're absolutely right of course, the distinctive and attractive comma ears would have likely been copied by others seeking to match the desirability of Osborn's work, and while I noted it was 'likely' to be, 'possibly' would have better served.
I think what is most interesting is the pre 1801 arms, and realizing that this cannot serve as a steadfast denominator in dating of weapons, again it presents as probably pre 1801. I am not sure when Johnston worked, or the others who also may have used the comma ear feature, or the faceting, but I have generally been inclined to pre 1801 and Osborn. It seems I have seen the comma ears on other M1796 light cavalry sabres that were with plain blades and probably a bit later, and thinking they were either officers 'fighting' sabres or for troopers, possibly yeomanry?
Again, great to have you posting again!!!!
All the best,
Jim