I was looking up the AM wiki here Scapa Flow (Covenant) | Ars Magica Wiki | Fandom, especially this bit intrigued me:
"the Norse Magus Yngvar, unable to master anything but the barest rudiments of Hermetic Magic, began to train apprentices, all of whom were assisted by Niall and Biluous, becoming a unique mystery lineage, the Sons of Yngvar, within Ex Miscellanea which endures today, incorporating the old runic secrets into their otherwise Hermetic Magic."
...it seems to imply that there is some mystery cult with a script for the Hermetic Rune Magic virtue.
Can anybody tell me if this is official and in case it were, where to find it? If memory serves, the 3rd ed. Lion of the North shouldn't have any mention of things like mystery cults and I can't remember mentions in HoH: Societates, The Mysteries or Ancient Magic.