7. Time travel becomes possible, however traveling back in time opens a new timeline and the old timeline exists in the past of the new timeline unchanged. So we observe the old version of the timeline, wile there's an alternate reality where guests attended the party and another future rebased on top of that history.
8. Time travel becomes possible. They are willing and able to travel to the past. Our archiving and preservation techniques are adequate. They aren't allowed to tell us they are from the future or meaningfully interact with us in ways which might change the timeline (temporal prime directive).
Also, rebasing the future makes me think of time travel as git history.
Imagine the merge requests and the fights inside them
this would be a very unlikely scenario where in our current timeline there are no time travelers but there are at least one in each new timeline. If that becomes true it might be the ultimate vacations/retirement plan, create a new timeline where you are the only timetraveler
