I saw this when you posted it, but haven't had the time to do the digging I needed to do in order to respond....today I was able to get to it.
I have a similar concertina I bought on ebay around four years ago. That year, on a visit east to NY from his Kentucky home, Greg Jowaisas believed/believes it to be a Nickolds. Mine has the identical font/size/style of printing that yours does. And, from the fret work, though more sparse than mine, is of a similar style. My serial number is 1258. Same round steel rods(flattened for the pivot post pin, screw, whatever), brass pivot posts. I bet the reed chamber walls are made of the same mahogany as the action board? Mine is. Is the low C on the left hand side marked "cc"? Mine is, picture below. Also Lachenal Type papers. And the same robust reed shoes(much beefier than Lachenal reed shoes)The differences....
Though it doesn't show in the photos(I forgot it was a point of interest), the hand rests are very slightly domed, not as much as a Lachenal, but not flat, either. Mine has machine screws, not wood screws. Mine also has a woodscrew going through the action board, into a supporting piece, into the hand rest. Your's doesn't seem to. Mine also, instead of the reddish material(I don't think of it as fabric) Lachenal used to cover the action, this has a type of very fine screen, like I have seen on some 19th century German made instruments. I wonder is the leather on yours was done by someone down the road? I think the majority of the differences in our instruments were due mine being a higher grade one, not a different maker.
I also have a typical 20 button Jones to compare it to. Totally different, un-inked/unburned, and much smaller serial number stamped in. Reeds and reed shoes very, very similar. But the low C is only marked "C". Also, the F#s on the Jones are marked as such, but only read "F" on the Nickolds. What does yours say? My Jones serial number is two different ones, the action board says 8579, and the reed pans and bellows frames are 8580! (someone was asleep at the wheel that day!) One side had a screw through a block in the action board going into the hand rest, the other side doesn't, but it does have a glued up hole, and a broken screw in the underside of the handrest.
I may be wrong, but this is what I think......I think that instead of this maker buying parts from Lachenal(reeds, reed frames, actions, all entirely different from Lachenal), this maker, presumably Nickolds, BOUGHT his parts from Jones! I don't think either of these instruments were made by Jones, because I think that Jone's with serial numbers that low would have had an air lever instead of an air button. But I could be wrong! Would Stephen C., David E, or Greg J. care to chime in? And, there are quite a few others out there with knowledge of this stuff, probably far more extensive than mine. Any opinions on who made these?
Thanks for your time and input,