I've been playing Horizon Zero Dawn while in a party with a friend playing it as well. While he went and did a lot of side quests in the valley, I explored and cleared the Corrupted Zones as I found them.
By the time he started doing these, he was roughly 7-8 levels higher than I was when I had done them. He encountered a couple Corrupted Glinthawks and a Corrupted Snapmaw in the Corrupted Zones in the valley, which surprised me as I encountered neither of these when clearing the same Corrupted Zones.
Are Corrupted Zones randomly populated or are the Machines generated dependent on something like player level at the time they're encountered?