This is a distraction. If you don't trust the NSA's oversight, then you should assume they keep everything for ever and taking issue with them being able to eavesdrop so easily.
If you do trust the oversite, it makes sense that they keep encrypted data around since they have no easy way of knowing if its from a US person or not. Once they decrypt it and find out it is a US person, thats where you should focus. It should be as if they collected US Person data originally and should count it as collected when they actually got it, not decrypted it.
As to the argument that the NSA could count anything as encrypted. Yep, they could. See point one.
If you do trust the oversite, it makes sense that they keep encrypted data around since they have no easy way of knowing if its from a US person or not. Once they decrypt it and find out it is a US person, thats where you should focus. It should be as if they collected US Person data originally and should count it as collected when they actually got it, not decrypted it.
As to the argument that the NSA could count anything as encrypted. Yep, they could. See point one.