My experince with the Yorkies is at about 10-12 weeks of age, for a few weeks, the weight remains about the sameor lingers and they loose that baby chub and get leaner puppy look. Then the weight starts coming on again. They just loose their "baby fat", so while they are growing body wise they are loosing chub and so seem to remain the same.
Your Yorkies will grow again, lol...I sometimes ask myself the same about my little Gracie and then I have to remind myself she is just growing up. The 3 x weight at 8 weeks and 2 x weight at 12 weeks is a pretty good estimate, but nothing is written in stone. It all depends on genetics!! Good luck,
not like it matters in the end, by the time they are grown we are in love with them and wouldn't change them for the world!! :P