A camera estate is usually finished long before it becomes useful. Screens get watched when somebody is free, footage gets searched when somebody has hours to spare, and the value of the whole installation quietly comes to depend on whether a person happened to be looking in the right direction at the right moment.
The gap is not coverage, it is attention. Nobody can watch forty feeds at once, and after an incident the recording that holds the answer is reviewed by scrubbing through hours of it. By the time the footage has given up what it knows, the moment when somebody could have acted on it has usually passed.
Everything below works with an installed estate rather than replacing it. The cameras carry on doing what they already do, and what changes is that a question can be put to them, and that something can be raised while there is still time to do something about it.