Thanks for the link.
It doesnt seem to say exactly what the dog has to have won at the show to be called "Best of Winners" though, but im guessing from the descriptions in the rules that it must be the same as our best of sex.
It is the best between the class dog that was winners (and the one that got points) and the class bitch (and the one that got points). And the Best of Winners gets as many points as the one that didn't got best of winners.
So, if the class Winners bitch got 3 points (known as a major) but in class dogs there were only enough for 2 points, if the Winners Dog then was Best of Winners, he too would get 3 points. We call that a cross over major.
LOL, I am sure it is confusing, but then I still get confused on your point systems with Challenges… gggg