welcome to TY. You might want to check out this thread
http://www.yorkietalk.com/forums/showthread.php?t=16045
it has a puppy growth chart.
so many breeders promise a certain size and you can not go by that. they grow as they need to, just like humans.
my yorkie, Ahia, had 4 puppies and I thought 2 of them were going to be bigger as adults. when I sold them I told the new owners I didn't expect them to stay small. but they have. even a 10 lber to me is not big in any way.