User blog comment:Suparockr/List of Plotholes throughout the series/@comment-1679409-20120729154938/@comment-1679409-20120729160256

That's a good point, but I would imagine there has been some time those events. For example, we know that "a couple of weeks" have passed between the Fall of Tiptree and the Fall of Thessia. There are at least three core missions between Priority : Citadel II and Priority : Earth. That tells me there is a good bit of time for the keepers to make at least some progress, especially considering it's to the Presidium.