[3FurryFaces]

Originally Posted by Breezeaway

In a closed stud book, the parents must also be registered in this or another registry for the breed that the organization maintaining the registry will accept (such as that in another country). This ensures that the animal is a purebred member of the breed. It also, depending on original numbers and management practices, can lead to an ever increasing level of inbreeding.
An open stud book, animals can be registered without their parents having been previously registered. This allows breeders to strengthen breeds by including individuals who conform to the breed standard but are of outside origin.
An open stud book may eventually become closed once the breed type is deemed to be fully set.

Hmmm... But some Biewers breed back to traditional yorkies and they don't meet each others standard.