May be wrong info but I saw this on 6speedonline regarding the GTR.
I have spoken to one of the R&T editors, who was kind enough to take the time to discuss the provenance of the GT-Rs used in testing. That conversation relates to this thread as follows: Nissan provided 3 GT-Rs for testing to the automotive press. A white, a silver, and a Black one. The black one was damaged somehow and was kept in reserve for parts. All three cars are US spec, but are definitely pre-production, and are classified as "engineering test cars", which is the only way they are legal for registration and operation on US roads. Once their lifecycle is done (90 days), they go to the crusher. This explains the caveats by C&D, and MT regarding the performance, and the extraordinary dyno result produced by the silver car.
That SAME silver car, with Michigan plates, is the one now competing in the One Lap. It is therefore NOT a production car, and if the dyno is any indication, is making a lot more power than the production car's certified 480.
I agree with Wanderer Z06 that this has no real bearing on the OneLap since it's a run-what-you-brung race, but the GT-R fanoys have been claiming all along that a production GT-R is outperforming the stock Z06s and that is simply not true.
The R&T editor also said that this car is causing a major ruckus in the auto press and that some mags are rethinking their testing procedures with respect to manufacturer-supplied vehicles. Automobile reportedly declined to test the Nissan at this time because the cars supplied were not production cars. Expect that trend to be followed by others henceforward, he said.