from what i have read from my research on the subject is that Biewer Yorkies were bred from yorkies in Germany and Parti yorkies were bred around the same time in the US from a different stock of yorkies. It is also not as common to dock tails in Europe which is probably why Biewers have their tails and parti's do not. And in my opinion we should stop docking tails all together, (1) I love long tails and (2) it just doesn't seem very nice to cut off a body part for looks.
I consider my Somi a Biewer Yorkie, but she has a docked tail. But that could also be due to ignorant breeder not the actual breed of dog. I call it her little nubbin and try to grow the hair out so she looks like she has more of a tail, because her's is docked way too short.
