I knowThe point is that it's supposed to be past/TNG Data, not "present" 2399/2402 Data. If they didn't kill him off in Nemesis and he was playing current Data they would more than likely just age him up a bit, and that would be totally fine.
But the Data is not supposed to have aged yet. He's supposed to be the same Data that we have seen A LOT of for seven years. That's why it's a problem.