I have 2 old white 421s, one with the large Tuchel connector, and one with the smaller Tuchel connector. The mic with the larger connector is the older of the 2, and it most definitely sounds fuller in the low mids than the newer mic. The newer white mic sounds fuller than a recent black 421 but doesn't have the same HF extension. The easiest way I find to hear the differences is to use them to mic a dirty guitar sound.

Whether these sonic differences are as a result of aging is purely conjecture, as they were never new at the same time