The puzzle for me in all this is why would this particular symbol become a "decoration" uniquely on Lehigh county rifles? That is, Lady Liberty or Columbia isn't associated only with Lehigh county at this time. So if it is Lady Liberty, why wouldn't this carving show up on rifles all over the place?
That's the $100,000 question!
For the purposes of discussion I would tend to set aside those found in neighboring eastern Berks Co., and these tend to be much more whimsical in nature and perhaps more artistic license than representation. Peter Angstadt in particular seems to have adopted a cruciform shape which may represent Jesus, or something else entirely. A couple unsigned pieces clearly are meant to be Indians. And many if not most of the Berks pieces are what I would view as second or third 'generation' i.e. those seen on Stophel Long's work, he being considerably younger than the origins of the symbol (or I should say, 'apparent' origins) in NH County. Possibly, by the early 19th century, the underlying meaning or the "why" may have given way to simply an expected decorative form. All speculation on my part.
Broken record: the earliest I have seen are either Moll work or potentially Wm. Antes (the swivel breech), although the dating of both is in question. Moll's work is tough to date and so is the swivel breech. What appears to be the earliest in my opinion is the Levi Wells pistol, the brass barrel of which seems to have been cast by Moll and is stamped underneath with both "Moll" as well as the liberty figure. I find it interesting that the figure on that pistol is hidden under or along the side of the barrel, and is stamped almost as a 'trademark.' The pistol generally is taken to be late War-era or possibly immediately thereafter, and it is believed Wells may have passed through or near Allentown sometime between Sept. and Dec. 1781 while commanding a cattle drive from CT and/or Long Island to Frederickburg VA. He was already a Colonel at this point and it seems likely that he acquired it at this time.
