I just gotta say: this is a great site. I have gotten more traction here on a simple forum question that doesn't even include images than weeks of emailing pictures and stories to music/antique/junk shops. I'm waiting for a few downsized pics to transfer through the ether to my computer, but then I think I'll be able to get up a picture of the whole concertina, with the "DOUBLE ORGAN" sticker on it (it's not a contemporary "sticker" but I don't know what else to call it) visible, as well as a pic of the reed assembly from my single furtive look inside.
...I will say, given my experience with instruments of all sorts, the construction I've encountered begets a "passable beginner level" vibe--I don't get the feeling this was an object meant to have parts replaced or a great number of things done to it before the owner basically leveled up to something better. I'm somewhat of a tinkerer and wouldn't mind the opportunity to have a bit of a Frankenstein machine -- it allows me to learn a great deal about the mechanics and construction of a thing as I go on the journey of fixing it's failures, so learning it's not something of great value would honestly be the best case result
Aforementioned images should now be included in the reply. And yes, the "GERMANY USSR OCCUPIED" text is certainly in English (as is the sticker).