The only thing is it's still unknown at this point if these changes in the driver are directly responsible for the difference in sound, or are merely indications of one version or another. There could also be differences in the voice coil, magnet, dampening foam, etc. I say this because if it is actually caused by those non-visible aspects, there might be some overlap where some "bass heavy" pairs have the appearance of "bass light" pairs, or vice versa. One only needs to look at the K240 Sextett nonsense and how long it took to get any kind of consistent delineation between versions, because of things that initially seemed to belong to one version would occasionally be found on other versions. At this point we know with clear certainty there is a difference in sound between earlier and later pairs, but we still do not know with certainty what causes the change, and whether it occurs at a specific point, is a gradual change due to wear and tear on the manufacturing equipment, or is even multiple, slightly different sounding versions leading to a larger difference over time.
Frankly I don't care enough to try to investigate it any further myself, but if someone wanted to start compiling a list of serial numbers including version (or presumed version), as well as the various aspects of each pair (opening size, diaphragm type, PCB type, etc) it probably could become possible to narrow it down better. I'm at a point in this hobby where I don't want to deal with the research and cataloging of AKGs anymore.