There is an important underlying issue here.
The NSA's legal doctrine is that collecting and retaining data is not a search under the 4th amendment, and so has no legal protection. Querying their data for information on a person is a search, but as long as that person is not a US citizen, there is still no 4th amendment protection. If they query data for a US citizen without a court order and then find out that it was a US citizen, their policy is that they immediately throw away the search and forget that they did so. Since there was no intent to search, they think that the accident is OK.
But any query that intentionally gets information about US citizens, no matter how minor, is a 4th amendment issue. Therefore, for instance, a query to find out how many Americans were accidentally searched would violate the Constitution. (This is not a hypothetical example - they refused to provide exactly that information to Congress on that rationale.)
Therefore they have built a system that stores data about all of us, and has safeguards to throw away any unconstitutional searches. The safeguards may or may not be as hard to circumvent as they claim. (I'd guess not.) But I'm sure that any attempt to find out will be met with the state secrets privilege.
