Otherwise it would be even more difficult to calibrate each driver as is. They do have to calibrate all the drivers in the construction process anyway, because tube length and placement will vary slightly from person to person. However those differences are measured in millimeters.
Since your ear hasn't changed, that means even if they had replaced all the drivers, the position of them shouldn't change dramatically for no reason either.
It's just easier to tell if the circuit board has shifted, because the board is small and thin.