Jehovah's Witnesses... is there a contradiction here?

I understand that you believe that when a person dies, he simply stops existing. No spirit anywhere... nothing. I also understand that Christ was the first-fruits of them that were resurrected (1 Cor. 15:20-22). If I remember correctly, you also believe that Moses died... that his life did reach an end. With that said, how did Moses manage to appear to Christ on the Mount of Transfiguration if he was dead but not yet resurrected?