It is probably part of the latch assembly. Whether it is a GM goof or a supplier goof (i.e. the supplier wasn't making the latch assembly correctly) I have no idea. But I can see how it would go unnoticed on the vehicle assembly line.
Silly question I know, but is it even possible someone could own a vehicle for three years and never realize it was missing the secondary latch?
It's not like it is missing a bolt or two; the entire assembly is just not there. Did they all think that when they pop the hood, it goes up without having to release a secondary latch was, like, a great new feature?
Honestly, I am surprised people can count to four to make sure all their tires are there.
Even if they are too dumb to ever pop the hood, is it possible their mechanics never noticed? The dealer mechanics never noticed? The plant inspectors never noticed?