These are what we call the 'YMMV items.' Things that some people find in this work. We call them 'your mileage might vary' because not everyone sees these things in the same way. This starts discussions in the trope lists, a thing we don't want. Please use the discussion page if you'd like to discuss any of these items.
Fridge Horror: When briefly talking to Harry about what the Denarians did to her she says only they did "things". Harry comments about having been there and his own experiences. Unfortunately the only incident Harry uses the term "things" about was a heavily implied rape by Bianca's people back in Grave Peril, which, given that Ivy is naked, leads to questions about exactly what was done.
More Fridge Horror: The fact that Nicodemus, had he not taken the bait and sought to capture the coins and Sword, would have given Thorned Namshiel's coin to Ivy ... and thus, unwittingly handed the Archive and all its knowledge over to the Black Council. We know it's the Fallen, not its host, who's in charge in Namshiel's case because of how he's referred to, so if Uriel is right about him, Cowl's crew would have gotten the god-caliber agent they'd been trying to produce in Dead Beat.
Harsher in Hindsight: When it is all over, Harry is resting on the Water Beetle after being rescued from the ice cold lake water. Because Thomas gave him dry clothes and hot coffee, Harry tells him he will leave everything to Thomas in his will. Thomas replied, "Cool. Next time I'll leave you in the water." Roughly two years later, Harry would be shot off the bow of the Water Beetle and falls into the waters of Lake Michigan, where he dies.