Can't speak for the 744 but on the 75/76 the overspeed discrete is supplied from the Vmo/Mmo calculator within the DADC. This does not have any flap position input into it.
There is not a flap position input at the Clacker/Wailer, or the master warning module to modify the o/speed discrete either so I would say that avoiding a flap overspeed is down to good airmanship.
Of course there is a flap load relief system which operates but only for full flap positions (flap 30) driving the flaps to flap 25 if airspeed exceeds 170kts.