Isn't it normal to see the 'standard and included options' for a car on the window sticker? If the 4.10 gear option was selected as well, then that too would show up on the window sticker.
The REAL Question here (in my mind) is how would that gear option be implemented in the factory? It certainly wouldn't be with modifying a 3.73 gear rear in the assembly plant, so the question is: Would the gear plant pull a 3.73 rear (already built if it has the BU code stamped on it already) and replace with a 4.10 gearset and go thru that same original setup work AGAIN? WHY would they not simply ship one of the already built 4.10 gear rears which was stamped with the normal 4.10 stamping??
I think it's more likely that at the time of the car's BUILD, there were no 4.10 gear rears available in the assembly plant (a fairly rare option), so it was assembled with the std 3.73 rear. When the car arrived at the dealership (without one of the options - which did happen pretty often), then the customer/dealer agreed that it would be updated (modified with the 4.10 gear set) at the dealership. I'd like to see the ENTIRE window sticker to determine if there's more information there that might help explain the issue...