Does the score screen at the end of the level include hostiles that you HAD to kill. I just finished the high overseer mission, took really long, thought I killed no one, but the score screen said there was 1 hostile killed. Now that I think about it, maybe I didn't HAVE to kill anyone to complete the mission, hopefully I got a save near there to see.
Really enjoying this game so far, I'm so glad I've chosen to stealthy route, I'd have completed that mission in a quarter of the time if I went all out killing.