I'm no lawyer, but I would think that if they had a reasonable warrant that go them into the townhouse, and they found child porn that has been in his possession in 2019, then statute of limitations doesn't matter. You can't possess that stuff. He did. Up until a few days ago.
Excellent point. Kiddie porn has no expiration date. Photos taken 20 years ago will get you sent to prison the same as photos taken yesterday.