Search does not include historic items.
Search does not include closed items (issues, impedimets, ..) from historic sprints.
I need to know the way an impediment was closed months ago and it seems it is impossible.
Statement from Kunagi Team
Search does include closed, but not deleted entities. You will not be able to recover deleted items.
One exception to the rule are deleted Stories that may, as of today (04. Feb 2014) in certain cases be marked deleted but kept if still needed. But I would not depend on this; the "feature" might disappear soon in the context of performance optimizations.
Issue is closed.