Has anyone had any noteworthy campaigns set in an alternate history? I'm giving consideration (eventually) to a campaign where Innocent II's papal court was infiltrated by an infernal agent who managed to "lose" a large portion of the interdicts he leveled against various regions 9France, England, etc.) so they would not be lifted, and in fact remain in effect in 1220. Also considering a revision where the Cathars' allies (since the Cathars don't fight themselves) are winning the Albasinian crusade...
My group is currently playing in a completely ahistorical uncanonical setting. We decided that we wanted to advance the starting year to 1715, and play in the Triamore saga. We also decided that unless something specifically had to change for game mechanical reasons then it did not change. We changed nothing about the virtues, flaws, character creation etc, except:
you dont need a score of 1 in Artes Liberales to be literate, and you can master 1+ Artes liberales writing systems as opposed to just Artes liberales. It is assumed that a basic level of schooling is available to most people.
Generally the advanced timeline allows us to play in a setting where nations are more consolidated than they are in 1220, and that makes small scale warfare less feasible because it can very easily escalate. That is entirely to our liking and forces diplomatic solutions to problems. We also assume that the mundane world is a lot more capable of responding to problems than what is the case in the base setting.
Regarding hermetic magic, no extra breakthroughs, no major wars, expansions, etc have happened from 1220 to 1715, all of the conventional history from 900-ish to 1220 has been stretched to instead occur from 900-ish to 1715.
We follow real history when it suits us. The reason for the advanced history is because some players wanted to play in a more contemporary setting and some wanted to play ars magica. So far it has worked out great. Soon I hope we will begin exploring the industrial revolution, set to occur in the netherlands rather than in england (assuming that england exists in a recognizable form in our setting).
Thebes: the Faerie God Athena is currently in control of Athens. So, this is something we're trying to diffuse before a new crusade happens.