Can't tell you exactly how many are out there, but I got my white M92 in January (?) 2012, while my girlfriend got black version around January this year.
The biggest hardware difference I noticed was the little joystick on the right: while mine can be moved in 8 directions (N, E, S, W, NE, SE, SW, NW), hers only moves in 4 (N, E, S, W). Also the new stick feels more solid and has better haptics.
