True Dudley Lab Puppy Weight Issue

Question
I have a true dudley male lab puppy that I obtained at just 6 weeks old.  He was the runt of the litter, very small when I got him.  He is now 12 weeks old and only weighs 15 lbs.  I feed him 1.5 cups twice a day of a high end puppy food (Zamzow's Grandma Z's Puppy Chow).  His vet says he is perfectly healthy, shots and worming are good and up to date and to continue doing as I am.  I'm concerned, because you can see his ribs and the top of his hip bones stick out.  He's very active and playful, mild temprament (calm) for the most part, has normal potty, acts just like a normal puppy...  However, he doesn't gain the typical 2 lbs per week as regular lab puppies do.  Do Dudley puppies grow differently?  Should I be cocerned about his physical "ribby" and appearance?

Answer
You shouldn't be able to see his ribs, see http://www.longliveyourdog.com/twoplus/RateYourDog.aspx  Usually it is no problem getting Labs to eat it if they need a little more food.  Guidelines are only a place to start.  So feed him a little more.  Keep checking him as above and adjust how much he gets to maintain good body condition.  It is very important not to over do it and let him become overweight.  It could be he will turn out on the small side for a Lab.