Strange on that first link. It looks like a J3380B. Where are the other J serials? If there were 3000+, seems like we'd have seen another one by now. The A/G# arrangement is very atypical and the trill guide is very heavy, also atypical. The marks with the circle and overlaid PM I have seen on other PM clarinets that were more typical. My Bel Canto has a mark like that. You don't see that mark too often but it is on some other Penzel Mueller clarinets.
It's fairly obvious where they got the "J" serial letter, less obvious where this might have been made, and far less obvious how many of these there actually are. So far, I've seen this one. Good find, although I did see the listing, just hadn't looked at the photos until now.
There are three possible candidates I could easily find for Jean Aubert, all prominent French people. One is an architect that died in the 18th C. Another is an engineer, died in 1984, and the last one is a popular French singer song writer that played a guitar, born in 1955. With Penzel Mueller production ending about 1956, we might want to rule out the songwriter.
The engineer guy is far more interesting to contemplate: "Jean Aubert was a French engineer. In 1961 he used the idea of the German engineer Julius Greve from the last century to describe a pente d'eau, (English: water slope) which was a way of moving boats up the gradient of a canal without locks." - Wikipedia
Frenchman, "borrows" a German idea that by force causes water to flow up-hill? That's elegant.

I'm thinking it's the architect / artiste fellow. That fits the typical French stencil brand tradition. It also looks like it could be a jab by Penzel-Mueller (NOT Frenchmen) at the practice of ambiguous French names appearing on clarinets. Where are the country of origin marks on that one? That would be my question if I could only ask one. The seller says US and of course it is marked New York, but so are most of the ones that also are marked France. The case is marked PM, but that case looks like a French case from about 1950. That type of handle on a rectangular box is typical of Malernes and other French clarinets.
You asked what I thought?
The Brilliante is completely typical of Brilliantes made for the US military, marked on the bell "US", and fits into the "M" series PM clarinets and extends backward that part of the serial sequence assumed to be parallel to the Korean conflict. That puts us closer to marking the 1950 beginning of that era of production. While the military might have ordered the clarinets in advance of 1950 or ordered more after 1953 has to be considered, but the date range of those Brilliantes marked US is definitely in the era of the Korean conflict. Somewhere between M5497B and M5898B is the date 1950, and finding 5898 narrows the window by about 300 Brilliante models. Of course it tells us nothing about Empires, Bel Cantos, or the other models because these weren't preferred by the military.