Vd/Md are the maximum demonstrated limits which form the hard upper limit for aircraft performance before you become a test pilot. You should not use these numbers in normal flight, because they were obtained and measured using instrumentation specially calibrated for accuracy. Your Vmo /Mmo numbers give you a small safety margin to help keep you out of dragon territory, whether it be 20 seconds of 7° nose down beyond Mmo, or a few extra knots from an off calibration airspeed.
The 747 going into San Francisco mentioned earlier this thread suffered tattered tail feathers from flutter and significant other damage. It pulled significant excess G on recovery. The FDR did not return much good data due to interference.
Those of you flying subsonic aircraft, need to believe in those limit speeds you have been provided. Swept wing aircraft really do pitch down when transiting M 1 accelerating and pitch up when transiting while decelerating. If your flight control system isn't intended to control this transition, then things may end poorly.
