Not entirely sure if this is a red herring, but there was a time when you could enter the sewers into the tighter path that led to a dead end... That stuck with me for some reason, that room is the only room I can think of that has no significance whatsoever. I'm of the opinion that there has to be something there, but after looking it over for a while I'm not sure, but I still can't rule it out either. I do think you're on the right track with the numbers though, I had the same thought myself when I encountered the puzzle, and I'm reasonably sure that the numbers are obtained one per chapter. I'm not convinced with any constellation either, but your reasoning is sound.