"The company complied with a classified U.S. government demand, scanning hundreds of millions of Yahoo Mail accounts at the behest of the National Security Agency or FBI, said three former employees and a fourth person apprised of the events."

Your theory is that Yahoo scanned hundreds of millions of accounts for the NSA, but the NSA isn't doing / hasn't done anything with those billions of emails. Your premise requires that the NSA come into possession of a truly massive load of data and then never touches it at all. That's absurd.