I understand that IP addresses are not reliable in pin-pointing a person's physical location. The inaccuracy is attributed to multiple factors. The IP could be from the DHCP pool and shared between many devices. The IP could be a proxy.
So far in the early part of the book, the IP has already been used twice to identify the physical location of the computer user.
I refuse to believe the IP was employed as a shortcut. Stephenson does his research. So I'm not ready to accept it was accidental or necessary just to move the plot forward.