My guess is that they didn't have enough information to effectively act on it. They probably knew something was going to happen on those days, but not exactly what, where, or by who. Hard to stop a specific murder if all you have to work with is that someone dies somehow at some point during that day..
>I wonder if "complete control" means absolutely responsible for the acts?
Q team is "in control" but they are not omnipotent. Events of significance have happened in the past that Q team were not able to prevent and instead had to react to.