Joshua and Moses predicted where they were going to be buried after they cacked. They were right. That is, if they actually wrote the books that the WTS says they did.
This is the whole point. We have no proof one way or the other. We have no proof that the bible books were written by so and so. We have no proof that the prophesies were added afterwards, and we have no proof that they are original and true. As with all other bible questions, there are excellent arguments to be found both ways. It drives me nuts.