All of Clark's history has already unfolded naturally by the time we've reached the Legion timeline.
Except that when he and Booster are temporally displaced by the ring, then he was no longer there to create the history that Rokk, Imra and Garth knew when they first come back. History was changed. This is the point that I am (unsuccessfully) trying to make here. It would be no different than if Clark got aboard a spaceship and traveled at the SoL until a thousand years had passed outside the ship. He wouldn't have been around from the point that he entered the ship. History would've changed the moment that 'Superman' disappeared. History, in this version of the 31st century, should show that Clark/Supes mysteriously disappeared 1,000 years earlier and never showed back up. History will be RESTORED when he's deposited back at the point he left, thereby being able to create the future history that the Legionaires know.
BTW, thanks for the theory regarding Skeets' new visibility. Sounds good to me.