Or there are just two torpedo tubes, but at least four bays dedicated to the storage of torpedoes. Not combining the storage system into one big warehouse helps contain damage, just as in modern naval warfare. But any of the bays can send a torpedo to either of the tubes.
Or there is just one torpedo bay, which can be in various states of readiness. 2 is a relatively low one, suited for inspections and burials, while 1 and 0 would mean almost total inactivity; 4 means battle readiness. Thus, the sign flashes from 2 to 4 when the ship goes to battle.