This arose from some comments on another thread, but it is entirely separate to the discussion there, and so warrants a new post.
That's an incorrect view of canon. You seem to be of the opinion that canon is a subjective thing, and that people can decide what they accept as canon and what they don't. This is not true.
canon, n.
1. a. A rule, law, or decree of the Church; esp. a rule laid down by an ecclesiastical Council. the canon (collectively) = canon law: see b.b. canon law (formerly law canon: cf. F. droit canon): ecclesiastical law, as laid down in decrees of the pope and statutes of councils. (See Gratian, Dist. iii. §2.)
2. gen. a. A law, rule, edict (other than ecclesiastical). b. A general rule, fundamental principle, aphorism, or axiom governing the systematic or scientific treatment of a subject; .e.g. canons of descent or inheritance; a logical, grammatical, or metrical canon; canons of criticism, taste, art, etc.
It might seem like I'm being pedantic here (because I am...), but I do think it is an important point. Canon is not decided by the fan base, it is decided by the line editor ("decrees of the pope") and effected by the books published ("statutes of council"). David takes the very sensible attitude of not permitting the authors to make tangential references to pre-5th edition material, nor to introduce into canon material which is not pertinent to the matter at hand. For example, when writing Lion and the Lily, the authors did not mention by name any Provençal covenants. Naming covenants from previous editions would have been as wrong as making up new covenants; anyone with a saga in Provençal would be justifiably upset, and the authors of the Provençal tribunal book would have been constrained. However, it is perfectly acceptable to name covenants from the Rhine tribunal, or the domus magna of House Ex Miscellanea (both canonical thanks to pertinent books).
Why? Because we paid money for them, and we consider them valid until something replaces it. In fact, every single ArM5 game I have ever played successfully relies heavily on 4th edition cannon and concepts. My entire saga is based on the 4th edition concept of House Flambeau.
That's fine – even encouraged – but it is not canonical. "4th edition canon" is only canon for the 4th edition game. You might be relying on previous source material, but that material is no longer canon, and you can make no claims about it being so. It is virtually impossible to run a canonical saga – I certainly don't (we are based in the Loch Leglean tribunal). But the purpose of canon is to form a common reference material for a) authors to draw upon to create a coherent world view, and b) storyguides & players to use as a rules base and source of stories. It is not meant as a constraint for storyguides/players, who can, of course, use older material or non-ArM material as they see fit.
Only a select few adhere to the idea of “ArM5 only”, and they tend to be people who had the opportunity to write ArM5 cannon. If and when I ever get to write for the line, I will be one of the few in the old cannon camp, saying “they make me write it this way, but personally I like the old way better”. To me, the genius of ArM5 are the vast improvements in the rules; NOT cannon.
Again, it is not a case of a select few adhering to an "ArM5 only" canon. The opinions of the players and authors are irrelevant, since canon is objective, not subjective. There is only one canon, and that is the one that is published for Ars Magica Fifth Edition by Atlas Games. How much adherence to that canon there is varies greatly, and that's where the "select few" come in.
Whether previous editions of the game reset canon, I'm not sure; certainly there was material used in 4th edition that was first mentioned in earlier editions, but this could have been reintroduction into 4th edition canon or reinforcement of existing canon.
Furthermore, "old canon" can be made current canon. This has been done with most of the domus magnae of the Houses, for example.
Personally, I find the "clean slate" attitude of 5th edition canon refreshing and useful. It's not that I want to invalidate former material – I rely on it greatly in my own games – but it is useful as an author to not feel constrained by material from previous editions that no longer works or is not to my tastes.
Mark