I'm not an expert in this. But I know a breeder who has had close to 200 puppies, and the last one had a short tail. He's the only one out of that many. I believe that it is an anomaly. Just a bizarre thing that happens once in a great while, but doesn't mean the puppy will "have something deadly wrong with it".
I think that is what you are asking.
And if a big breeder wants to pipe in and tell me I am wrong, then I defer to their knowledge.