I'm pretty sure it was three reviewers when these queues were originally created. I never really understood why it was lowered to just one. Sure, that cut down on the robo-reviewers casting three upvotes on everything because there wasn't a No Action Needed button, and review audits didn't exist at the time either. Now that we have all this stuff, can we bump it back up?
At this point it seems like we've cut out the abuse of users destroying our site with the upvotes and stuff,now they're destroying it with the No Action Needed button. Really, it only takes one good reviewer out of the bunch to make something happen with that post. A single user reviewing it (flagging, editing, whatever) should still dismiss it from the queue. Once it's flagged or edited, there's really no reason for additional people to be looking at. Presumably that person took care of the problem. However, I think it should take the full three No Action Needed reviews to dismiss it legitimately as not requiring any action.