All cities change on a daily basis, so no map can or does try to keep up. Entropy happens. LC would be useless if it was that important. Butcher made a narrative decision to have the device be broken. It's when he makes the reveal that is most important IMHO. The story is over and he's recapping and explaining as part of the denouement. Why tell us then, when it no longer makes any difference?
And can someone explain to me Lasciels's purpose in the plot? She doesn't do anything useful, at least on the surface. Does Butcher think we forgot about her?
She jump scares Harry in the car just before he is hit.
She throws a hissy fit when he uses LC.
She talks to him in the church.
Use the threshold the way Butcher does. He uses it to nerf magic. If he wants a character in then the threshold lets them in. If he wants them out then they are out. And if the story demands it there is a workaround.
She is there, she is a source of information, more so than Bob, more importantly, and it is easy to miss, she is becoming Lash. There is one line, one line only but could be the most significant line in the whole book in my opinion, has huge implications for the plot down the road in future books. Harry is in the chapel of St Mary's on page 288
Lasciel's voice came to me, very quietly, and sounded odd. Sad. It is beautiful here.
That,in my opinion was a turning point or the signal of one, Lasciel is changing. Lasciel would never have made those observations, she was all about manipulating Harry to see things her way even as she was helping him. This was regret, an awakening of long lost memories of what it was like before her Fall. Lash was about to be born, not too long after that she begins to help Harry play music, even compose, something else she has never done since her fall, supposedly hadn't missed but forgotten how much pleasure she got from it.