I will leave the Paxinosa association to Bob and Scott - they know far more about the archival material in question than I. Also, my personal interest in both 19 and the shorty is not for whom either may have been made, but whether or not Albrecht made them. The tricky thing here is that the two separate issues are somewhat intertwined, because my thoughts for what they are worth:
(1) I do not doubt in any way that the two pieces were made *at the least* in the same shop, and very likely stocked by the same man.
(2) If it can be somehow proven that 19 is the gun mentioned in the documented diary entry, well then there really should be no doubt it was made by Albrecht. If this is so, as I stated previously and as Rich has stated, it sure raises a number of interesting questions about other assumed Albrecht or Moravian-attributed rifles.
(3) I personally have no qualms whatsoever about dating either rifle as early as the 1750s, or as late as the 1770s. In other words, there is nothing I see that could preclude 19 being early enough to fit the bill for the diary rifle. The lock looks reconverted with a siler cock and frizzen but the plate and shaping of the lock sure looks early enough also.
(4) As noted, nothing about either piece looks anything like any of the other assumed Moravian rifles. Of course Oerter's dated rifles are 1770s so they are much later, and rifles such as Marshall's rifle or the Lion/Lamb which seem earlier may at the same time be perhaps 1760s, so even they may be at the least 10 years later. Things can change - suppliers, style etc. Bob has illustrated that they were purchasing parts and furnishings: can not the style of the furnishings dictate somewhat of the style?
I do not see either of these rifles as in any way similar to Albrecht's lone signed much later rifle. That rifle looks very classic early Lancaster-ish or Dickert-ish. These rifles almost seem to have a whiff of a French twist in the style of the stock shaping, despite being very German. Other than a lack of a stepped wrist, I do not see any comparison between the assumed-Lititz rifle and these two earlier rifles.
In regard to the box cavity - that is of course a very German way of cutting a box mortice, and an early method. Possibly it became passe as time passed? I don't have an answer for that. There are other little things that don't quite mesh with what I see upon the other attributed Moravian guns, the manner in which the lock 'beavertails' are designed jumping out somewhat. Again, however, perhaps things changed over time, or perhaps guns such as the Marshall gun and Lion/Lamb were actually made by Oerter. I think the Lion/Lamb is an Oerter rifle anyway.
It is certainly very possible that both rifles are Albrecht pieces of the 1750s. Unfortunately, much more work needs to be done in attempts to definitively determine if there is in fact a signature on the shorty, and if it is Albrecht's. If they are Albrecht work of the 1750s, it's possible they may be the only two pieces of his that have survived other than the later gun assumed to have been made at Lititz. Many questions there.