Not logged into PPRune for some time John.
With caveats: a) memories blur after half a century, b) this was an area of Aerospatiale responsibility
Worth remembering Concorde instruments and autocontrols were analogue - simplicity rules!
Vmo is manufacturers choice subject to some conditions, principally that Vmo cannot be greater than the structural cruise design speed Vc
So:
The low speed cutback could well have been a birdstrike precaution. The relevant rule is "The empennage structure must be designed to assure capability of continued safe flight and landing of the
airplane after impact with an 8-pound bird when the velocity of the
airplane (relative to the bird along the
airplane's flight path) is equal to VC
at sea level"
The low supersonic "sloping" Vmo/Mmo was derived from performance considerations. The performance obviously depends of the variation of drag with airspeed and Mach No, together with the thrust variation with altitude and Mach. The objective was to choose a flight path which maximised the increase in energy height per lb of fuel consumed. From these sums one could generate a nominal boundary which gave the basis for a scheduled Vmo. The upper limit of this was defined by possible aeroelastic problems at the Vd/Md arising from the statutory upset from that point