The AMA Nats and a local contest are two different things.
At the local level, judges, event directors, and even Contest Directors find ways to complete and nobody minds. The theory is, "we never give up an entry to get a judge".
But the Nats (and FAI Team Trials) are a whole different thing. Maintaining integrity and the image of integrity is all-important.
In categories like Speed, Racing, and Combat, it's no problem for everybody to compete and take turns judging. We do it all the time.
But in events that are judged by personal opinion (Scale, Stunt, and Carrier), "I judge you/you judge me", just won't cut it. Let's assume we have five events and two event directors: So Event Director A judges events 1, 2, and 3 and flies events 4 and 5. Event Director B does the opposite. This is a hypothetical example, remember that! If the two Event Directors end up winning all five events (or even place highly) some of the "losers" will sense the smell of home cooking.
It's good to discuss these things on a theoretical level now, so they won't come up in reality later.