Well you can look back at any one of the new puppy threads and see what a 13 week Yorkie puppy looks like. Except for the coloring they looks basically the same when it comes to the hair. They are fluffy. And for the breeder to say that the hair will grow in. If I am not mistaken if you are a reputable breeder you know exactly what a 13 week old yorkie looks like.
Here is a link to some of the groups dogs in their younger days
http://www.yorkietalk.com/forums/my-...-then-now.html