I don't seem to understand why people say that Bethesda doesn't make decisions for previous characters in other elder scroll titles in regards to story or lore. Reading that UESP on Umbra talks about what the Neravarine does AND the champion of cyrodiil at length. what if "My character never killed umbra in morrowind"? This is in regards to a question I had on what side would win, stormcloaks or imperials according to lore. people tried to make it seem like it wouldn't matter when it came down to the lore and that they wouldn't tamper with the player choice/decision but they always do. I mean, also look at Sheogorath.. he is the champion of cyrodiil. What if my character never went to the shivering isles and told Sheogorath to shut it?
They have to do this because some people will do a given questline and some won't... its effects in later Elder Scrolls games cannot be both felt and unfelt. The "canon" is that the Champion of Cyrodiil became Sheogorath, that the Nerevarine obtained Umbra, etc. Regardless of what you specifically did in previous Elder Scrolls games, the starting point of Skyrim has to be the same. They aren't making a thousand divergent universes.
It's not like we can pretend the Oblivion Crisis never happened for those who did not finish Oblivion's main quest.