It's nice to think that each product was so carefully thought out that it required its own set of custom drivers, but from a business standpoint, why make a different driver for your $800 speakers (CDM 2SEs) than for your $1200 (CDM 1SE) speakers? And in 5 or 6 different speakers, NONE of the mid/woofers have the same electrical properties? This is a real head scratcher for me.
I worked for a speaker manufacturer that made there own drivers and I can tell you that having slightly different drivers for each model is fairly easy to do. More than likely the engineers would mix and match from the many various parts that they were already using to fine tune each driver to it's intended use. An example would be using a smaller magnet with a stiffer surround to alter the parameters.
Sorry to hear about your B&W driver.... If pushing very lightly on the bottom of the surround eliminates the buzz you may just have a sagging cone. If that's the case you can try rotating the driver 180 degrees.