Hi Cassius,
I haven't seen you post before so welcome to BPO. I have had dobermans for about 17 years now, and currently still have one bitch along with a dane and dane/IW mix puppy. As to your question, can I ask a couple to clarify things?
Is your puppy a bitch or a dog? Females are generally smaller than males to begin with.
The other thing is, how does it look? Is it bright eyed, with a nice shiney coat, healthy pink gums, can you see ribs or is it unusually skinny? How does it act? Normal puppy bouncy, curious and happy, ready to play, then sleep like the dead, or is it lethargic and mopey all the time?
All of those are better indicators than weight, because it can really vary from pup to pup. Dogs get growth spurts, just like kids, and the puny 40 LB grade schooler can turn into a Liv Tyler look alike.
The scrawniest dobie pup I ever had developed into a 110 lb monster who was the sweetest, gentlest dog I ever had.
It sounds like you have a good relationship with the breeder, they are really your best resource if you can ask them. They should be familar with the way their lines should develope.
Sorry this is kinda long, but I hope it helped.
Stella