Another way i can think of which might be the same as LM's comment which is term I haven't heard of before.
Stall speed is linked to the amount of G you are applying.
If you take the Stall speed in level flight and times it by the root of the G you will get the stall speed. So as you increase the G the higher the stall speed which may be above your overspeed.
As for how they measure it.. There are two main ways. A little flap on the leading edge which gets lifted in the airflow and the more modern method of having an angle of attack sensor which measures the AoA and sets off the alarm at a pre determind limit which is changed if you have iceing limits.