(A) Prove the primary reference contains an “enabled disclosure;”
(B) Explain the meaning of a term used in the primary reference; or
(C) Show that a characteristic not disclosed in the reference is inherent.
Non of these apply to your example. The definition of novelty is - for practical purposes - that a single source had the invention before you did. Adding to that source by using another source defies that purpose. There needs to be prove that an invention was known with all characteristics claimed before the filing. Therefore the three exceptions only allow another document if it had auxiliary purposes.
Proving enablement doesn't change the invention, it merely proves that the source is valid. Explaining a term doesn't change the reference, it just shows the reference actually says what the examiner says it does. The third is probably the most difficult. To validly use a second source against novelty the source would have to clearly state something like “all cars have wheels“ when “A + a car“ is used against “A + a car with wheels“ for example. “Some cars have wheels“ would probably not be enough as it doesn't prove wheels to be inherent to cars.
However, for all practical purposes, the definition of obviousness during US examination is, in my experience, “combining two references leads to the core invention (use more references for not so important elements) even if they clearly don't fit together unless they explicitly state they can't be combined.“
So a second source will in almost all cases impede non-obviousness. And what you described -the claim is only fully specified if source 2 is introduced- is a by the book definition of obviousness.