Anrein was not part of the clan. He specifically says as much. there is no precedent for a four mage clan. Even if there were, and there isn't, you're the one that's always keen to point out how not all clans are the same. That a clan who's Keeper used Blood Magic for vengeance against people who never harmed him, and who lied to his clan and put them in danger for his own selfish reasons once a year, to flaunt other Dalish traditions wouldn't be a surprise. STILL not a retcon.
There is a precedent, despite the fact that you consistently ignore it: Aneirin. He was the fourth mage in a clan when it already had Keeper Zathrian, First Lanaya, and Elora. He was welcomed into the clan as a boy, grew up among the Dalish (they even know him fondly as 'Aneirin the Healer'), was taught elven magic, and was even given vallaslin when he became an adult. When we encounter Aneirin, he is wearing Dalish leather, and refers to the gods; while he says he decided to live out among nature as an adult, he makes it clear it was of his own volition, and that he follows the clan because he feels indebted to them.
You're also missing the main point that the 'three mage recton' is inconsistent with how the Dalish were previously portrayed, and it's in complete contradiction with what Merrill explicitly said, as well as her own codex entry.
I wasn't actually thinking of any specific instance, just your go-to tactic of using optional protagonist dialog as proof. In order for that to be slander, it would have to be untrue. Which you just admitted it wasn't by giving an example. So, thanks.
For someone who claims that I do that repeatedly, you seem to have a strange inability to actually cite any example where I've done so, while I pointed out a particular time where I addressed the main character's dialogue in conjunction with a codex entry that affirmed the same information, since I disputed that only the Chantry had a historical account about the war with the Dales.
Anrein is completely optional content. He does not exist in worldstates where you do not have that conversation with Wynne. No one else ever mentions him, he isn't an unexplained NPC in the game world, there are zero signs pointing to him without the trigger, and he's never referenced in other games. He's no more a part of the world if you don't talk to Wynne about him than Starbaby is if you don't have Warden's Keep.
Encountering Aneirin is optional; Aneirin himself exists regardless of whether or not the Warden personally meets him, particularly as it's an incident that helped shape who Wynne became. You're confusing game mechanics with the narrative, but your line of thought would be like arguing that Goldanna or Marjolaine don't exist unless the Warden personally met them, which also wouldn't make any sense.