(or "Night Of The Living Document")
Despite what a lot of people might believe about comics fans, we do understand that the world of comics isn't real. We know that none of the stuff depicted in the pages of the Fantastic Four or the Avengers actually happened, and that history has not been influenced by the Skrulls, the Celestials, or the Kree. (Jury's still out, though, on whether there's a big bald guy in a toga watching us from the moon.)
It can be useful, however, to pretend that the universe of Marvel Comics is real, because it shares similarities with the real world. It has a geography (with Latveria, Wakanda, and the Savage Land) and, more importantly for purposes of this column, it has a history. By looking back on all of the many issues of the many titles Marvel has published, you can compile them into a single grand story, simply titled 'What Has Gone Before'. Or, if you're Marvel, you're having your 25th anniversary, and you're feeling a bit grandiose, 'Marvel Saga'.
The Marvel Saga shows everything that happened in the Marvel Universe, starting with the first flight of the Fantastic Four's rocket-ship (and, simultaneously, the leader of Alpha Flight designing his first version of the Guardian armor), moving on through Iron Man's first adventures (and his first meeting with Jim Rhodes, the man who would one day replace him), and concluding Volume One with a definitive account of the life of Captain America and its defining tragedy, the death of Bucky Barnes.
Yes, now you're realizing what those parenthetical comments have in common. There's a big difference between the real world and comics after all. Namely, that no matter how much archaeologists and historians search for new information on the past, they don't have to worry about the past actually changing. Conflicting accounts, lack of detail, those are all bugaboos in the real world, but once something's happened, it actually happened and we all know it. In fiction, that's not true. If Ed Brubaker decides that Bucky's badly-injured body was instead fished out of the North Atlantic by the Russians and used for decades as a brainwashed assassin, then that's what happened. (Until, of course, someone else decides that he was a Skrull all along. "Dueling retcons" are common when dealing with comic-book history.)
Marvel Saga finds itself in an awkward position, in that sense. It's trying to present itself as an accurate and definitive history, but there can never really be such a thing in a fictional universe, because the narrative changes with every flashback, time-travel story, and "everything you knew is wrong!" shocker. Its storytelling engine is to treat the Marvel Universe as history, but it's undercut by the demands of an ever-changing universe.
So does this mean that the Marvel history should never change? Should the Marvel Saga be the Bible of the fictional universe, the history that's "nailed down" so that we can move forward? Probably not. There's always something new to say about the past, and looking back can make for an interesting story. Certainly, the new Captain America wouldn't exist if Ed Brubaker hadn't decided to weave a new narrative around the gaps in Cap's history.
Which isn't to say that the past should be treated as wholly mutable, either. There's a lot to be said for simplicity, for a past that everyone can understand and get up to speed with quickly. The more convoluted a history is, the harder it is to emotionally invest in the character's present. Look at the Vision, a character who went from being "an android created by Ultron" to "the armor of Iron Lad, a younger incarnation of Kang the Conqueror, made sentient by a download of the consciousness of the android made by Ultron out of the body of the original Human Torch (which was temporally duplicated by Immortus) and the brain-patterns of Simon Williams, aka Wonder Man." Adding retcons into a character's background is like digging a mine. There's lots of valuable stuff in there, but if you hollow the whole thing out, it's going to collapse into a big sinkhole.
In other words, the Marvel Saga shouldn't be a Bible...but it does do a nice job of telling you where it's still safe to dig.