This seems like a rather minor part of a conversation Carlos had with Harry, at Marcone's Castle before Ehniu showed up.
Carlos - "How's Karrin doing?"
Harry - "Like always, but slower and grouchier."
Carlos - "I heard what she did. Went hand to hand with Nicodemus Archleone and survived."
How did Carlos or anyone from the White Council know about this? Was someone sitting under a veil watching the whole thing play out? That seems highly unlikely. I don't think Rashid saw it through some time travel message shenanigan's. If he had it's unlikely he would have told anybody else unless he believed it was necessary to do so.
I'm going to eliminate Nicodemus and the Genoskwa from the list of people who would have spilled the story. One's on the run and the other would rather kill a human than talk to one. That leaves Harry, Murphy, Michael and Waldo Butters. Charity was in the safe room with the children.
Murphy was pretending that her injuries occurred in a traffic accident and Harry would have backed her up on this. That leaves Michael and Waldo and Michael was in the game a long time before that day. Long enough to know there are some things you don't share around the campfire.
I think Waldo Butters shared the story of Murphy going up against Nicodemus with some of the people on the paranet. He wouldn't have done it out of maliciousness, just a lack of understanding that some things need to be kept under wraps. Unless, it was Mr. Sunshine and that seems really, really unlikely. Do you have a different solution?
A couple of other questions come to mind. Shouldn't Harry have been surprised by Carlos' question? If Ramirez knows about Murphy going against Nicodemus, how much more does he; and the White Council, know about the break in of Marcone's vault? For that matter, what about the rest of the major players in the supernatural world. For example, shouldn't Lara know the same facts? However, even though Carlos knew that Nicodemus had been set up, he gave Marcone all the credit for doing so, which was incorrect. Marcone and Hades provided the bait. Mab was the real brains behind the plan and Harry made it happen. Do you think Carlos realized that Harry was involved, because it didn't seem like he did to me? If you want to reread this passage, it's in chapter 25, page 238.
To be honest, I believe Jim was getting so rushed with his last two (one) novel(s) that he didn't apply the polish we are used to. Several times I suspect he just wanted to put the idea on paper but didn't really go through the whole process of working out how that information should come out naturally, and we as readers are highly sensitive to that. It's hard as an author to get that right as it is but when under pressure I am not surprised that things blow out a bit.
Take Harry's conversation with Bob early on in BG about Reality starting to break. The scene is almost word for word something out of one of Jim's interviews or Q&As - Harry is the questioner and Bob is Jim. Why would Harry say to Bob (in-universe) "Ferrovax the Dragon" when Bob would already know who he meant by saying Ferrovax and Bob probably knows more than Harry about what Ferro really is? And why would Harry bring up a conversation from 20 years ago with a being who wasn't even present for it (as though they were) to ask about this? It was almost as if Jim wanted remind not just the audience but also himself of what happened in Grave Peril when Harry and Ferro first meet.
The conversation would have made more sense (in my opinion) if it read more like:
"Bob, when I first met Ferrovax he told me his true form would crack the Earth - did he mean Reality?"
"Yes, Harry you moron. Did you really think he meant physically crack the planet's crust with his weight? It only took you 20 years to figure that out!"
Or something like that. Instead it came off as clunky, ham-handed exposition. It wasn't the usual standard of Jim's writing at all.
Another example is Dresden's mysteriously deep and practical knowledge of how the Arma Christi (Weapons of Christ - the artefacts he retrieved from Hades' vault) seem to work. How on earth did he know how the plaque worked? It's not like that knowledge is just everyday information (there is no lore that suggests it in our world either). If it is common knowledge in Harry's universe (which would be extremely bizarre) then shouldn't more people know? If it is in fact the rare knowledge that it most likely IS (and should be), how does Harry come to possess it? It's not like Harry could just test this stuff either. It's almost like a scene was missing where Harry needed to seek out information on the artefacts of the Redeemer. Same with the Spear of Destiny? How does Harry know it's a spear to everything (I assume that means nothing can stop it)? And what a crude use of it too. A mundane stabbing tool. Surely the Spear of Destiny (supposedly a weapon that makes the holder invincible) can be used better than for a mere tactical contest? We are talking a thing connected to the fundamental and supreme power in the universe. And while we can put it down to Harry being a brute yadda yadda - we know now that Harry hasn't been the brutish "engineer" that Jim wanted him to appear as for a long time. We have seen that he is intelligent, crafty, ruthless, diplomatic (at times) and thoughtful. Harry's should know more about his weapons, that doesn't bother me. But how he came into that knowledge does. It almost appears to just pop into his head. Who knows, maybe it's another type of intellectus (clever tool for Jim to use too).
The Wizards judicial proceedings are modeled after Star Chambers and the Wardens after Death Squads. Why Jim chose these particular models escapes me.
Jim has always made a bit of a point through out the series of the dangers of large organisations that impose rules on others. I suspect he himself was channelling his own feeling about bureaucracy (particularly in relation to his rather harsh treatment by the university administration - not the professors - something he mentioned in an interview). It's somewhat thematic too for such an old organisation, so it works in-universe too. Currently he has Harry seceding from the White Council under the guise of this is for the best etc. Maybe it is, time will tell. But it's certainly heading towards the destruction of the White Council and the rules-based order they have helped keep. There may come a time where Harry might regret this. Perhaps he is even being nudged to do this. These days Harry sounds a lot like Cowl when he talks to and about the White Council - but with less haughtiness and style.
I still think the "killing humans" is BS. It was a battle. It's like killing someone in self defense. It shouldn't be a reason to expulsion, or death sentence, or anything.
You also have to consider Harry's expulsion was not really about whether he broke the rules, but because people wanted him out of the Council. For varying reasons. Some on the Council think he is a legitimate danger (and clearly there is a big reveal coming about Harry's dark origins and possible future). Some want him isolated from his former allies so he will be easier to manipulate. Some just want him removed so he can be killed easier. It's politics after all.
