Glad to finally hear someone else say that in fact "it isn't the reeds" that make most of the sound of an accordion. Sure, the stiffness of the reeds influences the sound, and the gap between the reed tongue and the hole in the reed plate it goes through influences air consumption and how much "hiss" there is from spilled air, and it influences how cold it can get before the reeds stop playing (because the somewhat shrunken reed tongue can no longer go through the much more shrunken hole in the reed plate. (It's steel versus aluminium... expansion rate different by about a factor of 2.)
I played and worked on several seemingly identical Bugari Artist Cassotto 285/ARS accordions, which contained reeds of the same quality type but from different manufacturers... and they all sounded the same. Yet, take for instance an older Pigini Sirius and a Hohner Gola, from the same era, both fitted with Salpa a mano reeds, and their sound is vastly different.
I firmly believe that most of what makes the sound of an accordion is the reed blocks: how wide they are at the base versus at the top, i.e. are they more towards rectangular or more trapezoid with narrower top? An old Hohner Morino has nearly rectangular reed blocks (seen from the end) and for instance a Victoria has reed blocks that are much narrower at the top. That means the resonance chambers inside the blocks are very different and that causes the same type of reeds to sound differently.
Other than that what's impeding the sound to come out, i.e. what's under the grille and where are the holes in the grille... that too has great influence. Register mechanisms block (higher frequencies in) the sound of what's underneath them. Solid (versus open) parts of the grille do the same, giving Giulietti accordions a special sound (with just an oval cutout in the grille). Some things under the grille have great influence, like a sordino, and some do very little, like the "tube chamber" in some Titano accordions. Likewise the sound of the bass depends a lot on the construction of the bass compartment (holding the mechanics) and the position and size of holes to let the sound come out. The sound resonates so much inside the bass compartment that even with high-end accordion microphones a single mic capsule inside the bass compartment is enough to capture the sound of all the notes, regardless of where they are on the reed blocks. On the treble side the "compartment" under the grille does little enough that about 4 or 5 mic capsules are needed to capture the sound more or less evenly. (The very commonly used three-mic Sennheiser modules simply do not give a sufficiently even sound.)
The woods are another important factor. The Hohner "Metalbau" accordions have a terrible sound (but liked a lot by some...). A wooden case gives the sound more body, resonating midrange frequencies more and dampening higher frequencies somewhat.
There is so much to the accordion construction and its influence on the sound that is visible and perhaps even more that's invisible. When looking inside accordions there are invisible mysteries. For instance: when I look at the cassotto construction of a Hohner Morino N or S series and put it next to that of say a Bugari, I simply cannot see anything that might explain why on the Morino (made by Excelsior) the M register sounds more mellow than the L register whereas on the Bugari it's the other way around. To go further, the Gola also has that mellow M register yet again nothing inside looks more similar between the Morino and the Gola than between them and the Bugari (or a Scandalli or a Pigini for that matter).
So when you say "Questions?" it's hard to make questions concrete, but there is a lot I do not understand about what part of which accordion has which influence on which aspects of the sound... And that is hard for me to accept, with my scientific background which makes me always want to understand rather than just accept what something is.
