Here are my thoughts on this matter. Just about every breed of animal on earth is a mix of other animals of the same kind. Almost every domestic breed of dog, cat, cow and horse etc, etc, etc, were engineered by man at some point by mixing other animals of the same kind to produce certain traits that the breeder desired. Once the traits the breeder wanted were achieved, the breeder kept that set of genes pure so he could faithfully reproduce the desired traits in the offspring. Some breeds of dogs, for example, were developed hundreds of years ago, while other were developed in the last few decades. I believe, when it comes to the standards of pedigrees or breeds, the only difference between some kinds of animals (like dogs) and other kinds of animals (like chickens), is just how man has chosen to classify them. A pit bull dog is just a mixture of different types of canines and a cubalaya is a mixture of different types of avians. The difference is, if you can prove it's ancestry, you can go down and get a Pitbull AKC registered, but a Cubalaya you cannot.
To the best of my understanding so far, I think a chicken is judged to be of a certain breed, not by it's ancestry, but by the conformity of it's physical appearance to a set standards set forth by a committee of people that decided (at some point) what the perfect representation of each chicken breed should look like. I am in no way an expert or even a beginner, but it is my understanding that it really does not matter how you get there, as long as you get there. It's the "how to get there" that takes the real knowledge and understanding, of which I am totally devoid at the moment (but I am learning, thanks to the kind and knowledgable people on this forum.)