But when they went back to find it in the Enterprise, it hadn't actually been created yet. The Pasteur created it and it ran backward, expanding as it went. That's why they couldn't actually see it from the Pasteur. Upon their return it was, from the anomalies standpoint, several hours away from being created.
And I'm not slagging on the episode, I think it was one of their best efforts. It just never occurred to me that the premise completely falls apart in the final 20 minutes until I watched it earlier today. Technically, the future Enterprise couldn't have played a part in the resolution since it hadn't even started yet.