One question which might arise is, if the short rifle can be proved to be old AA, why sign that and not #19? Especially given that the natives early on could be considered a primary customer. Probably a question that can never be answered.
This is a great question--and I'd love to hear a discussion about why researchers think craftsmen signed the barrels (or locks) or whatever generally. I wrote before that, at least in part, a signature served to indicate who was responsible for the work in case something went wrong. Sometimes such signatures or other marks were
required in later contracts. So in these cases, the signature doesn't indicate anything about pride in craftsmanship: it's required by external authorities so faults can be traced back to the makers.
It is often said that the lack of signatures on Moravian arms stems from the fact that these arms were built in a communal economy. In my opinion, there is no evidence for this claim.
Most hand-made stuff wasn't signed in early America--furniture, for instance, or paintings--and these other craftsmen weren't working in communal economies. There is no evidence that Moravian practice changed after 1762 (when the communal economy changed in Bethlehem) or 1771 (when it changed, sort of, at Christiansbrunn). The Moravian painter John Valentine Haidt didn't sign his history paintings or his portraits before 1762 and he didn't start signing them afterwards (he died in 1780).
The pamphlet to which there is a link above states as fact that signatures were "prohibited" due to the communal economy: again, no such prohibition existed, as far as any evidence has ever been found, and so this is one instance in which the pamphlet states
as fact something that is a speculation and, once one explores it a bit, an unlikely one.