I agree with all the points others have made about the FAQ possibly only applying to the US, 3 colors of white being available, and years being assigned differently in different places.
Just one other reason it's not necessarily a repaint- I believe there was a special order plan available in Japan where you could choose the color of the body, roof, wheels, and interior. Not sure when they started this, though, but it could have been when they introduced the targa and 16/17 inch wheels.
Lastly, in Japan they also have a "refresh" program. You turn in your NSX, they strip it down to the frame (not sure if they sand the old paint down to metal), replace all wear items (anything rubber), and repaint it in your choice of color. Seems unlikely they would miss the underside of the hood if this was the case, though =P
Have you looked at other hidden parts of the car for signs of a re-paint? Under weatherstripping, carpeting, grommets in the engine bay, etc. It would be a shame to miss out on a fine white NSX! My fav color too =)
Good luck!
Jeff