Yes, and I think a lot of people do, in person. I know I do, and I know the people I've talked to personally usually say, "Now these pens are birds I got from so-and-so and I've had them a couple years now and I'm working on -this- and -that- with them..."
I think breeding is too fluid to really do something like that. Every time someone chooses a mating, they're exerting their own ideas on the birds, and in time will either make them better, worse, or keep them roughly similar.
Now, I feel like there are some ethics involved. If someone asks...