I'm not mixing up ingame and real-life "before's", for the simple reason that in the post of yours I responded to you were comparing ingame history with ingame prophecy.
That's just not true. What I said was that it doesn't make sense to say "the Nerevarine didn't rule Vvardenfell, so why should the Dragonborn become Emperor". I explained that it doesn't make sense because the Nerevarine was completely unknown before Morrowind, so there were no anticipations of him becoming a ruler of some sorts. However the thing here is that the lore already has quite a few people called Dragonborn, and now there's this new Dragonborn who apparently plays a big role... so I said that the people who say he might follow the tradition of the other dragonborns do have a point that can't be easily dismissed by saying "but the Nerevarine!".
Also, when I said "the Nerevarine wasn't even known before Morrowind" and you replied "yes there were other Nerevarines" you were definitely mixing up the "before"s.
The facts of lore being existent before the development of the games is completely irrelevant to the discussion occurring between my post and the one I responded to. If you want to use that as your argument, do so, don't bring up that the Nerevarine was determined by prophecy while the Dragonborn has historical precedent, because that's a different discussion - the former is one which I couldn't have become confused in, because it was never one I was having.
I'm sorry, but you were the one who disagreed with my statement and then used a prophecy as an argument. I wasn't the one who delved into that, I was the one who tried to steer the discussion out of there immediately. I also didn't say the Nerevarine was determined by prophecy - I said that all the lore about him was merely prophecies (which have been outright stated as contradictory right at the beginning of the game, I believe), while what we currently have on the dragonborns is historical lore. The difference is that prophecies may turn out to be true or false, but historical lore we just have to assume is correct (unless there's reason to doubt it, and there isn't in this case, there have been multiple people who have been repeatedly called dragonborns) until we get new sources.