I disagree.. Remember the story is told in the first person, and Harry does seem to know
a lot. He wouldn't have survived this long if he hadn't. He used both Bob and Lash for information when he needed it, it has been critical to him when needed.
Harry has been lied to about his mother for most of his life.. By people he loved and respected, most of all trusted, from Justin to Eb... He has also suffered from PTSD from his encounter with HWWB to the killing of Justin, lots of stuff has just been blocked out of his mind. It's the mind's way of protecting itself.
Another mystery, in Cold Days Maeve says that Mab is mad and and intends to unleash chaos and destruction not seen since the fall of Atlantis. Like I know the guy is busy, but wouldn't you go "hey, might be time to ask what happened to Atlantis" to someone who would have the true story.
Or since he figured out that Maeve herself was mad, think she'd tell him the truth? Or merely her version of the truth? In any case what happened to Atlantis really wasn't relevant to his mission at the moment... Who knows, maybe off page or between books he did the research?