Bill may, or may not, have been the author of those concepts; our conversation on the subject took place at the KRA in 1992, so it has been awhile. Nothing I wanted to hear mind you, but horns do fit the advice of the old Latin warning 'caveat emptor.' I plead guilty to buying two grand carved horns for a lot of money, a long time ago, and found out that I had old horns with new carving.
To the orignial question, what does an old horn of that period look like. my take is that it is nearly impossible to tell without additonal evidence. Almost any common horn could be that old. As the rifles got fancier, some horn makers may have progressed in quality and design as well; think York, Berks, and Lancaster here, but in the early 1800s. Would like to hear from Alan Gutchess and Walter O'Connor here on this subject, but not sure we will. They have the answer, I am fairly certain.
Dick