Thanks for posting the MM and DMG sections.
I am getting my sources from the post I was directly responding to and the threads on the Greyhawk lore in the 24 DMG. I don't have direct access to either of the 24 MM or DMG lore (I only have the 24 PH and the 14 MM and DMG). So the posts I had seen said the cambions changed from offspring of humans and demonic parents to mortals corrupted by demonic forces with a d6 origins chart so it sounded like Iuz's origins as an old style cambion no longer fit.
I knew Iuz was a god in 24 Greyhawk and the ruler of his own kingdom but not whether they specified his parentage.
Looking over that d6 chart none of them match up to parentage, nor do the general cambion description parts match directly the way they used to in older descriptions so it is ambiguous whether that is just his notorious parentage and something else turned him into a cambion or that was what made him a cambion or whether it was a combination. I would not have called pre 24 Iuz a former mortal as his potential pre demigod status would have still been from being a demonic cambion due to his parentage.
Not sure I would classify the half demon son of a demon lord as a mortal until extra demonic stuff happens, it is sort of a fuzzy line there whether they would be classified as a mortal out of the gate or not. In AD&D they were cambions in the demon/tanari section of the monster books, in 3e they were half demons of type outsider and not humanoids.
Hellboy comes to mind as well.