Why did the despatcher not radio or call you and request a new loadsheet with the correct figures on?
Why not indeed! This points to a lack of knowledge on the part of the dispatcher. He should never have let that flight depart without a signed copy of the loadsheet and have contacted yourself to let you know what the pilot had said. The pilot should also have known better. Do you really think he would have taken the trouble to come back and sign a copy of the new loadsheet on his return...........
I would advise that you check the DOW/DOI yourself in y airlines loading manual once you know the crew config and before producing the loadsheet, just as an extra safeguard.