Maybe we're not understanding each other, because I don't think it's as complicated as that.
My assumption is that at new year's midnight, their Wii warehouse is empty. Any units manufactured before have been shipped. Any error in this assumption will cancel out if we assume they have the same strategy for both years (i.e. non-shipped units from 2007 get added to 2008 but the same number is subtracted later).
With that assumption:
At the end of 2007 all produced units are counted as shipped. The same thing would be true for the end of 2008. The difference between those two numbers is what was produced in 2008, not more and not less.
My Mario Kart Wii friend code: 2707-1866-0957







