First of all breeders should stop using males from CW lines
Maybe this will make people become more concerned about how pure their dogs really are. And I see no reason not to skip one heat of a female wih doubtfull blood - just till everything becomes clear.
I also understand, how terrible it is to understand, that your breeding female can be a mix, especially when she has children and grandchildren allready
Even thinking about such a possibility takes my breath away
Still, the right thing is to evaluate all the possibilities and to check twice if there are any doubts about that...