So I'm watching through halo lore videos in my free time and I've come across one that includes the gravemind talking with chief, the arbiter and the monitor. The monitor mentions that that particular installation has a success rate of 'X' trillion simulated and one actual. So that installation had been fired in the past? The only novel I've read is fall of reach which didn't touch on any of that I don't think. I was always under the impression that the proper firing of a halo destroyed the halo. That's obviously not right. So my question is, how many halos have been fired in the past?