Larger Diamonds at GKI presume they will find what they look for, hence the DMS design for the GK plant.
On the Other Hand, the Foxfire diamond out of Diavik (188 ct) was a lucky surprise. Would be interesting to see the probability of finding one that large in the 12 or so years of mining that Diavik has been operating, based on their size distribution projections. The 'experts' say that there shouldn't be diamonds that big in Canada, but here we are...
https://niceice.com/foxfire-diamond-almost-crushed/
https://www.bloomberg.com/news/features/2016-05-18/freakish-diamond-pulled-from-sub-arctic-ice-is-about-to-go-on-sale