The path from a source to an answer
Did the agent open a source that contains the expected fact?
A miss here means: the search never surfaced the right source.
After the improvement work. Bars at 02, 03 and 05 show the share of expected evidence still alive at that checkpoint; hatching is what was lost by then. The bar at 04 is different in kind: the share of questions that triggered a live check at all.