No they do not need to come from a PB EBD & a PB Boxer. A pb English/boxer puppy is considered an F1 foundation/1st generation hybrid. An F1b is a backcross- like my pup. His dad is a pb english, but his dam is an F1 valley bulldog. A valley to valley pup is an F2 or second generation and so on. Here is a handy animal husbandry cheat sheet if it helps: Purebred-A x Purebred-B = F1 Hybrid Dog F1 x Purebred-A = F1b Hybrid Dog F1 x F1 = F2 Hybrid Dog F1 x F1b = F2b Hybrid Dog F2 x F2 = F3 Hybrid Dog
Parents must be registered with the IOEBA. (Olde English Bulldogge Association) they are one of the better Kennel Clubs for answering questions and concerns. Their website is easy to navigate and if you call them directly they will answer your questions via real human being.