I suspect that Butcher has had a fairly good idea about Mab's destination as a character since day one. He's tuned it as he's gone along, but she was never written as the evil faerie. Butcher says that constantly, but what he writes is quite different. But the plot has certain elements that must be served. If the story is a mystery, then the central mystery must be solved within the covers.
The book has two. You are handed one mystery by Eb. Why didn't Mab retaliate? Then Rashid hands out the second mystery. Who is using Black Magic in Chicago? IMO as a reader these have to be solved in the book or the book falls apart. The narrative would be incomplete. That isn't to say that there are not other things going on. But the two central mysteries are solved.
Butcher encourages confusion for readers. He uses Bob very effectively as an unreliable narrator. Rashid's letter specifically calls out when the Black Magic is done. Yet he has Bob supply a red herring in terms of how and when Rashid knew what he knew. You may be sure that it wasn't that happy horse crap about getting messages from the future and paradox. Paradox occurs when you break cause and effect. Everything about the Black Magic was over and done with before the first trial.
In the case of the first example, Harry tells you what Mab expects. To be back stabbed by Summer. When he has the forces of Winter returning to the fortress he shows you that it isn't true and that Summer, in fact, is not out to attack her because of the power imbalance.
I have no idea what Mab is up to or where the backstory is going. I doubt Butcher does in detail. But the things I'm throwing out aren't about those issues.