Ironbutt57. Thanks for that pointer. My preference is towards exceedances based upon Vref - if and when a support call is needed. For various reasons the crew may elect to adjust the planned approach speed up or down, but Vref stays the same figure. It makes sense therefore to use Vref as the baseline. There are operators who mandate a support call at 500 ft agl on final. It may include a speed call-out and a rate of descent. For example "Speed Vref+8...Sink Rate 800 fpm." This is meaningful whereas a call of "Bug +2 based upon selected approach speed could be hovering on the danger area of Vref +20 limit where additives are large due wind gradient factors.
Overuns on landing are quite often the result of excessive threshold speed. In turn, excess speed is often due to wind additives (gradient and/or gust factors) that turned out in the end to be not needed. On long runways especially, excess speed over the threshold is accepted as normal because there is little danger of embarrassment. Some may regard this as careless flying and they are probably right.