Information!
The original Infiniti dealership that sold the G35x was very helpful. The G was sold in 2005, fully loaded, and serviced regularly at that same dealership from 2005 through 2007. They last saw the car in 2008 with 60k miles on it. The only remaining note says that it was at an auction. No other details were available.
The logical conclusion is that the car was traded in with 60k miles in 2008 to that original dealership, likely for a 2008 replacement, and the dealership was unable to resell it at that point, and sent it to auction. From auction, it likely was purchased by a used car dealership, where it went to a second owner. This second owner put the next 40k miles on the car, before it somehow ended up, probably as a trade-in to auction, at this current used car dealership.