1-He did not meet two of his friends.
Can't this sentence mean two things:
a-It is not true that he met two of his friends. Maybe he met more or maybe he met just one friend.
b-There were two of his friends that he did not meet. He met all the rest.
I would say that maybe "b" is the more natural way to express the idea it expresses, but I think "1" can be used instead of it.