After the nerevarine rids himself of corprus disease, he is immune to diseases and aging, but appearently disappears sometime between the events of morrowind and those of oblivion.
Now, would there be a possibility that the Hero of Kvatch (and perhaps later the Dovakhiin) would infact be the Nerevarine who has returned from Akavir, but tired of the fame and wealth, decided to start a new life in a new province and somehow got thrown in jail?
As I said, I'm not suggesting this as an explanation of what really happened, but I like the idea of (even if I'm the only one who knows) play the same character through all three games (and seeing as how he is not touched by aging, this might make sense).
Kindly awaiting your response
PS. First Post here, really looking forward to engulfing myself with the lore and immersing myself further within the universe of the elder scrolls.