Just a thought to those who are chipping litters for breeders.
Given the rate of dogs landing in rescues where chips are located but the owners have moved & not updated details etc, I would say that as implanters register these chips they should use the opportunity to register the chips under the pups KC name & in the comments box on the registration page state something like:
"This puppy has been sold with a return to breeder contract. In the event that contact details for current owner are out of date please contact (for eg) Lilliegarden St Bernards on XXXXX XXXXXX"
That way you (or the breeder) have a better chance of being alerted should the pup in question surface in rescue or a pound later in life