Hi there,
Reference of VS is for conventional aircraft and represents the speed when lift suddenly collapses(load factor<1).
The yanks use VS,so for example VREF is based on VS which cant be less than 1.3 VS.
Airbus and EASA use VSR (reference stall speed) which may be not less than VS1G (calibrated speed/aoa at which max lift coefficient is just before lifts start decreasing).
For example, vref cant be less than 1.23 VS1G for flaps used (1.23VSRO), VLS on airbus i think.
V2 minimum for example can not be less than 1.13 VSR ...