(Sarah of the Clue Crew reports from an AKC dog show with a new puppy friend.)  According to the American Kennel Club, only the offspring of a sire and a dam of the same unmixed breed qualifies as this
... Best in Show, At 
an All-Breed show, the only dog left undefeated at the end of all judging on that... [DOC] [TLE] Conditional Registration - American Kennel Club [PAR] ... the registrations of the litter and its members and their offspring are canceled.