But without a valid court order, the evidence collected by the NSA cannot be used against a defendant in a trial. If a defendant feels a court order was improperly issued, he can appeal his conviction on those procedural grounds.

If the data is not used in a criminal case, then there is no mechanism for 4th amendment protection and the spied-upon has no recourse.

Except that this isn't correct in the face of parallel construction. You can't fight the evidence at trial if it either isn't presented, or its origins are misrepresented by the prosecution, which is what parallel construction leads to. (You use the stuff from the NSA to find other stuff, and build a plausible story about how you found the other stuff. The illegal search is never presented in court, so you can't fight it; the other stuff is, but is should be fruit of the poisonous tree, if the full truth were told.)

1. Data is collected without a court order, by an otherwise trustworthy government (for the sake of argument).

2. Time passes and government policies change

3. Information that was previously inadmissible, and which should have never been collected in the first place, is now admissible.

When we talk about law, we can't just consider how the current government will use it. We need to restrict how a future government could abuse it. You see the same pattern all the time in software: Some assumption is made in an earlier version. The basis of that assumption becomes invalid after further development. Now the thing that didn't matter before gets a bug added to your queue.

>But without a valid court order, the evidence collected by the NSA cannot be used against a defendant in a trial.

Ostensibly, but in reality the FBI or local agency will use parallel construction to find another way to introduce evidence without even mentioning the NSA.