I dont worry about the littermate stuff my self, I have come across alot of differences in littermates, bird dogs or retrievers, just my opinion, one thing always remember in training any dog.......for every action we do there is a reaction from the dog, when there is a reaction that we dont want or expect, we as trainers have to figure out what or why, and how to fix. If a dog is nuts about a bird, a crippled out there floating and flopping is hard to beat, dont be scared to have some bigger rocks to pitch out be the bird, if the dog is questionable, or is swimming and panics, you will want good splashes. If it farts around top long, grab littermate and send it, let it get the retrieve, do not allow your dog to touch the other when it comes back in, have it leashed, he doesnt need to attempt to steal the glory, give him another chance later. Just thoughts that are popping in my head, later Jonesy