You might already know that products intended to be sold in the United States have to go through the FCC, a certification agency. Sometimes, these products aren’t final versions—they might have small differences, unfinished manuals, etc.
In the (vast) majority of cases, there’s nothing special, but occasionally, there are some amusing things. Given how messy it is, I probably missed some things. That’s how I found out that the AirPort Express was supposed to support hard drives.
There are also quite a few manuals with « Apple Confidential » stamped on them and red annotations, but I haven’t found anything interesting in them (and it’s quite tedious to check).