Its a BOT that is constantly changing so you will never get a 100% correct / reliable answer... Google Bot could get the link that you have NoFollowed from some other page.
Besides there are so may ways to hide where you are linking to or have the page that holds links blocked in ROBOTS.TXT
I hope you would agree that GoogleBot does obey ROBOTS.TXT ???
So there you have an example where Google would "blind him self with his own rules". Many legit reasons to limit BOT access. Duplicate content being the first one that comes to my mind.
(Like hiding the Print friendly copy of the page you don't want indexed!)
And how abut my argument that SPIDERNG / INDEXING the spammers page benefits him?
Google will try to "do no evil" but there are so many gray/gray choices they have to make.
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Could you tell me the real-life situation you need this applied to?
You are not linking to a P0rn site from a kids site?
