Hi @Anonymous,
I am glad you figured out the Xref in viewport mystery. Now, as to the titleblock one. (It would actually makes this much easier if you attached your drawings a, b, & C)
I assume that in drawing A, you have created your titleblock in modelspace. When you save this drawing it can now be inserted as a block into other drawings as a block. Alternatively you can also XREF it into other drawings. If you choose the latter method, you have the option of the option of using an OVERLAY method which means that if it is XREFed into Drawing B, then if you Xrref Drawing B into another file the tileblock reference will no longer show up. 
Is this what you are trying to do? if not, please attach your sample files so I can make a bit better suggestion for you.
Please select the Accept as Solution button if my post solves your issue or answers your question.
John Vellek
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