the weight should be more how much does the "frame" of your pup need.
Some yorkies are tall and long and some are more Cubby, that bone structure type can carrie more weight and still look really small... the fine boned tall yorkies may weight less but look a little bigger becasue they are tall.
What I did after Remy was "grown" is looked up how to tell if a dog is over or under weight and as long as she is healthy not worry about it so much. You can check the ribs, and the back bone feels and if they have a belly
For example- Remy charted to be 3.5 lbs. She was so very skinny! When she gained to over 4 lbs. I was so happy.. them she kept going and got a little chubby. Now at 2 1/2 years she has settled into the weitght that is perfect for her bone structure.. which is 5 lbs and she goes up to 5.25 lbs.. any more and she has a "belly" lol