You are correct, I see nothing on the exploded view that looks like these parts. That leads me to believe that they are from one of the 4 items that are listed as assemblies, and thus aren't exploded. The gas piston assembly can be ruled out. That leaves the Trigger assembly, Bolt assembly or the Bolt carrier. Could this perhaps be the parts that retain the bolt operating handle?
I''m just guessing here, but I would look closely at those three and see if there isn't an empty hole somewhere.
“Life is either a daring adventure or nothing." --Helen Keller
"Do not cry havoc when you should but hunt with modest warrant." --William Shakespeare
Glock Certified Armorer
NRA Life Member