Vatican Searching Issues

[Klyuch]

In the Vatican dungeons there is a water area where you can swim, there will be a sign "need a breathing device", but the location is essentially a dead end. Is this an adaptive sign that appears due to a bug or will it be possible to return to the Vatican with this apparatus later? By the way, I wonder - does anyone have bugs in the guide? I have completed tasks, but the guide still says that I have not collected all the notes. Or, on the contrary, I am missing 4 pieces of information, but the guide only shows 2 of them, as if there are many notes in the game that are not shown. I also collected 26 books, and 27 leads to a mini-library. I did not find the 27th book or does it not exist?