If the Vet is going by the teeth, I would go by the papers.
Why would the Breeder give you the wrong date?
hmmmmm As far as size, you can never really tell,
They come in all sizes, even if the parents are small
I've seen 10 pound Yorkies with 4-6 pound parents.
so you really don't know, but what you do know
is they all have really big hearts.