The fact that Google illegally circumvented the "3rd party cookie" policy in Safari suggests that they do care a lot about an individual's data.
Re:Ask HN: Splitting Browsers for Privacy?
by legacy2013 on Sunday June 16, 2013 @04:33PM
(#5889830)
They do, but they will most likely not track through means that are not efficient, which is true in this case
In reality, ISPs change your ip address a number of times over a year, so Google couldn't know when the change occurs without some extra knowledge (such as you being logged into your Google account, but that also isn't fool proof because you could log in any number of places).
Google probably doesn't care that much about an individual's data and would not invest the time and resources to build software to track information on the level you are talking about