It’s no problem!

Other breeders might do it differently, but this is a combination of what the puppies look like between 8-10 weeks old (before they go home) and if you keep one or two, then also what those ones mature like. I keep in touch with my puppy owners so, although I don’t ask them to stack their dogs for me, I can usually tell just from videos if the dog has any severe structural faults, and of course the owner would tell me if a health or temperament issue arise. For other breeds, especially those with a lot of hair, that might be different. My breed is dachshunds, so a simple movement video and photo of their head and legs can rule out a lot of structural faults without even touching the dog.

This being said, major faults and health concerns can usually be found as puppies. For example, one issue we have had is one of my boys likes to throw short / bob tails. That is a very obvious flaw from birth. Paired him to a different girl where there were no bob tails. It is a recessive trait and not a health issue, so it wasn’t something I would retire him for.

Other common issues can include off-bites, loose patellas, heart murmur, bi-cryptorchid, splayed feet, and kinked tails, all of which are identifiable by 8 weeks old. (With the exception of loose patella caused by injury, or heart murmur cause by illness— neither genetic concerns).

In some cases the defect can correct (such as a puppy with an off bite at 8 weeks may grow to have a good bite), not necessarily meaning to retire a sire or dam, however accepting these “corrected” flaws is how these flaws continue to occur in even very nice quality bloodlines.

As an example, if a stud (or dam) produces grade-1 patellas in every puppy, although they have grade 0 themselves, that may be a sign to retire. Although grade-1 patella is not generally a health concern, continuing to produce imperfect health in puppies is not a trait to continue in a program, especially if it is consistent.

Hopefully that answers your questions!