You could have a yorkie that will be bigger or you may have one that stops growing early.
Sugar and Candy are maltese, but maltese are the same size as yorkies and the weight is estimated the same. At 6 weeks old they weighed alot, not quite 3 pounds. Now at 7 1/2 months old they are 7 pounds and have not gained weight since they were 5 months old. Their brother from a different litter was the same.
So you never really know how they will turn out, just when you think you have it figured out, they end up suprising you.