It's a 1st-person-POV story, so Harry only "knows" what the author writes him as knowing... and as noticing, in the moment (for example, there's the scene where Lash reveals there was a veiled figure at the Ordo Lebes meeting); though Harry is a keen observer, e.g. Harry noticed Abby's medic-alert bracelet.
It is, what it is, right?
But most of all, Jim himself attests that Harry is an unreliable narrator, and that Harry has a fairly simple & "straightforward" perspective, and mostly doesn't grasp the subtler (and more-correct) nuances of many situations & individuals.
Or more to the point, the author is giving himself wiggle room for changing his mind later in a long series or CYAing for his own mistakes that his "Beta Readers" might miss. So it all has to be taken with a grain of salt. I just think too many times it is a convenient excuse for posters who fail to adequately back up their own posts. If they can't prove their point the fall back line is Harry is an unreliable narrator..
Early Mab was written as the stereotypical "mythical villain" figure, the archetype and prototype of all Evil Queens (and Kings, &c); later we see that she's cold&hard because she's Winter, but possibly the single mightiest champion who's fighting on behalf of Creation.
But Harry's early perceptions of Mab,or of Morgan for that matter, don't make Harry an unreliable narrator. They were accurate as he saw them at the time as a young inexperienced wizard. When we first meet Harry he is a young wizard in his mid-twenties, a lot has happened to him, the characters, and the world around him in the last 35 years, and with them his perceptions Though he writes in first person, he writes not as a historian beginning the first page of the book," back in 1982 these are the events as I remember them.." No, his tale reads in first person, in that time period, as he perceived it in that time as a young man. I bet if you were to try and narrate a story about your life at 25, even with a daily diary, you'd do some correcting about the people you've met and how you saw the world at that time, at 50 you see the people you have met and the world around you differently. So for as he saw it at the time, right or wrongly, I think Harry is quite reliable.. That doesn't make him always correct, but for that moment as he saw it, he was.. Now often he will correct or admit he was wrong about events and characters as the series goes along. Events, information have changed his impressions of characters like Mab and Morgan in addition to his own maturity.
Harry's "unreliable" narration is from a place of ignorance, & an unrealistically-simplistic perspective.
No more than any human perspective, looking at the series as a whole, I think you can say Harry's perspective is a hell of a lot less simplistic in the last five books, from what it was in the first five.. Harry's narration is reliable for the time period he was writing in, it has shown mental and emotional growth over the series. His world has become more complex, he has a character has become more complex and matured.
"When I was a boy of 14, my father was so ignorant I could hardly stand to have the old man around. But when I got to be 21, I was astonished at how much the old man had learned in seven years." -Mark Twain.Mar 24, 2015
The same can be said of Harry..