Did King Arthur and Merlin Exist in Mythic Europe?

[OneShot]

@ErikT

What you or some other player decides about what is or is not in your version of Mythic Europe, has absolutely no bearing at all on what is canon or not.
Which official sourcebook something appeared in is also irrelevant for the matter.

Arguing about canon in ArM5 has a tendency to end in a mess. With over 40 books, it is both necessary and hopeless. See here and ff for an example to keep in mind.