But if you know what is in the breeding when your breeding for certain traits you can match up similar traits alot easier.
But without doing skills tests on all dogs being bred, you do not know if they carry or have lost that critical trait. Unfortunately most breeders of hunting and working dogs, take a male and female of a breed they have access to and breed them together, just for profit, with no concern on whether they are actually good enough at their job to be bred.
To make it even harder, most very good dog won't throw as good as they are and some not so good dogs produce better than they are.
Good breeders have to have a keen eye, excellent memory, creative mind, tons of determination and some luck.
Keith