Yep, like I keep saying, over the normal life of a single user, they keep working, but the discoloration isn't a blemish, it is a chemical deterioration, a compositional change. There will be few original Glocks passed from father to son. If they are, they were little used, not very old, or have had partial rebuilds to keep them like new.
I'm not attacking them, you don't need to defend your use of them to me, I'm just telling you the reality that a plastic gun has a limited lifespan built into it, extended by the use of steel parts at critical locations.
The tests in the video can only show durability and operational comparisons between guns over a tiny fraction of time.