Why would they be stating the number? How can they know if they intimidated or prevented attacks by mere existence? Statistically, mere police patrol presence r

Why would they be stating the number? How can they know if they intimidated or prevented attacks by mere existence? Statistically, mere police patrol presence reduces crime, which is not directly related to detective work. But, TSA is kind of parallel to surveillance, my question was about whether we could possible judge the success of that, and other intelligence in the most secretive of government operations.