2 part parcel shelf - did it confuse anybody else?

In case this confuses anybody else, the parcel shelf is in 2 parts with the first and obvious oblong piece mounted in front of you as you open the tailgate. I asked my vendor about the second piece and even gave them a photo of the part number and they told me that is was the parcel shelf from another vehicle and that I should throw it away. HOWEVER, they've come back today saying that's all wrong and the second, curved parcel shelf fits into the tailgate itself and then dovetails with the first piece when you close the tailgate. Fortunately I hadn't thrown it away and fits really easily know that I know where it goes. Feeling a bit daft as its pretty obvious now I look at it! Probably normally they've both come pre-installed but I was thrown by the second piece just laying there in the rear.