Even some of the best breeders and "conditioners" in the goldfish world cannot guarantee that a fish or a group of fish will spawn each and every year - or even spawn ever! One of the prettiest fish I knew never did - and others wait for years. There was one perfectly gorgeous Bristol Shubie who waited 7 years and then, out of the blue, produced a wonderful set of babies - with many winners in the group. Go figure.
I guess what we learn from this is that all we can do is try to do our best. The fish and Mother Nature take care of the rest.