and how do you "get" one?

i.e. - If I get a letter through the door from some dark government place accusing me of doing something, and I can prove the only way they could know that is to have taken "two or more unrelated (and unclassified) pieces of information and put them together" could I not just claim that it was a "secret"? Preferably with the help of the *fact* that no new "operational databases" had been created.

Surely, if IIRC, one of the definitive reasons for a database to exist in the first place is to link all relative information and so an "undiscovered link" could only have been revealed if there was a second, unlinked, database involved.