Good observations. I'd forgotten that you work for a speaker manufacturer.I'm gonna push this a bit farther. I know with PA speakers, weather comes into play. At work when testing some cabinets, we must calibrate the computer everyday to accommodate for atmospheric pressure. If we don't, the cabinets will fail the frequency portion every time, unless the atmospheric pressure is the same as the default setting on the machine, which it never is. The machine defaults at 124.0 bar. Our facility is about 1100' above sea level. The atmospheric pressure there is typically 123.5 to 123.65 bar. High and low pressure weather systems as well as temperature and humidity alter this even more.
Now I am not a sound engineer. I build and test the things to the tune of about 15,000 - 20,000 a year. Been doing it for over 5 years. And I work directly with the engineers. There is more in play with the sound you hear coming from it's source than just a turn of the knob or a hit with a stick. Did the weather change? Did you add something new to the room? Is your environment overly dusty (live on a dirt road)? Did you move the sound source? Did you clean your ears today? The considerations are endless.
So sure, the sound can change, but what else changed in the equation to alter said sound?
Bought a new K Custom Dark 17 and almost returned it because it wasn't opening up as nicely as my 16 and 18 (the other two would "crash" with much lighter hits). But after playing it only a few days it now opens up like the others. Is this common, especially after such a short time?