Tail length is determined by who does the docking. I find that most often, when vets dock the tails (as opposed to breeders that do it at home), the nubs are quite a bit shorter. There is a spot on the tail where it narrows, and that's where it should be docked. Some breeders prefer longer tails while others like shorter ones. My first Cocker hardly had a tail at all, but my show dogs have longer tails.