That's all a good point, but I'm pretty sure our character *can't* be from elturel. It's not the only place tieflings come from anyway, they just get born spontaneously sometimes due to demonic influence in their bloodlines. So we would likely have had very different experiences. And again, it's very possible that we ourselves don't actually know our subrace.
The Elturel thing was also just an example, since a dialog response arose in reference to it. I can't judge that one hundred percent. I only know that as a Zariel Tiefling, I have the appropriate magical abilities such as Searing Smite, which sets me apart from the other Tiefling subraces. So I wouldn't want to deny the ability to not be able to judge my Tiefling subrace myself.
But if Zariel can plague Karlach with nightmares where she carves her name into her body, or Karlach says that she was one of her champion Tieflings with much more fighting power that she no longer has, then I wonder to what extent Zariel can still access (Zariel) Tieflings and take away their abilities? I don't know if there are similar mechanisms at work here as with Dorn Il-Khan and his Patron Ur-Gothoz (BG 2) or Warlocks and their Patrons?
