Why are three chess sets needed for Kriegspiel and dark chess? Wikipedia states that three chess sets are needed for Kriegspiel and dark chess. Is that actually true? I can see how having three sets would make things a lot easier, but couldn't the referee simply reconcile the two sets directly, without using a third set? Or am I missing something?

Are three chess sets strictly required in order to play Kriegspeil and dark chess (without having to keep permanent track of the game state in anyone's head)?
I've never actually played Kriegspiel, but I've read a bit about it, and after what I understand it would be like this:

At a very minimum, two boards and one set of pieces are required. As the players only have access to the pieces of their own color, both players can share one set of pieces. However, they need a board each.

However, unless the referee is a very good player, he will probably have trouble detecting everything if he has to look back and forth between the two boards. Therefore, it's better he has his own with all the pieces on it. That adds up to three boards and two sets of pieces.

I can't see any reason to introduce a third set of pieces.