up to 40 is single flash WDR...
41 and higher are double (on some models even triple) flash WDR...
single flash means that sensor is doing one exposure per frame...
double/tripe means that sensor is doing two/tree exposures per frame, but second one is much shorter that the main one (to catch very bright elements)..
Image processor then combine both frames using WDR algorithm.
this allow to catch very bright elements (like car lights directed into camera) without overexpose the image..
simple (single flash) WDR is always more natural...
full (double flash) WDR is always more digital looking / over sharpen ..