Let's play a game: Save the Ancients!

[Vyrerus]

None of that makes sense, and the short story changes nothing except confirming whether we are in a "timeline is able to branch to support an old and new version of events" story or a "time traveller is exempt from the effects of a self-inflicted grandfather paradox" story, in favour of the former.

It makes as much sense as anything you've proposed, and yes, the short story confirms exactly what I've stated. It creates a second timeline, not a branch. It's not a branch, because the traversal relies on going to a space time that no longer has a coordinates within their own universe. This exempts their machine from being able to affect their timeline, since it needs those spatial coordinates (and it remains a great mystery as to how they even got them, since they're also dimensionally separate from The Source's universe and space time). The short story is the proof that their timeline was completely unaffected.

Branches for timelines come from second to second instances of time, and are already infinite and chaotic. You don't need a time machine to cause branches. They will result from any variation or hesitation in choice or chance.

The choice to try to change causality by traversing time causes a separate and new timeline, when dealing with backwards time travel. This is because the impetus for your traversal is linked to your past. You can't change your past at all, because it will fundamentally alter the casual links that lead up to your motive for the traversal. Particularly true if there's no way to account or plan to reverse for the changes you make.

Even if that's not how you view time travel, the short story introduced multiple timelines by having the 8UC remain unaffected by their traversal. This means their machine went to a parallel past. Not a shared past. For it to be a shared past, the short story would have to not exist, much like how the 8UC would have to no longer exist.

In other words, SHB's use of time travel concludes that you can change other timeline's past, but you can't change your own timeline's past. Which, with regards to Endwalker and the thread, means that the WoL could change things in the past but it would be in another timeline entirely.

Which Endwalker then takes the stance that a conjunction between two time periods has formed, resulting in our beloved causal loop, while still trying to have its cake and eat it too by having the WoL rewrite the past by showing them influencing things through Elpis sidequests. (This is why it's just Writer Fiat, and there are no real rules. This is a repeal or willful ignoring of the SHB precedent(in order to have fun, because there is nothing concrete about time travel, it is all theoretical and quite paradoxical))

You like to say that the story operates under the rules that changing the past just makes it so that the timeline revision is what always occurred, but that is not what occurs when there are multiple timelines. It doesn't even occur that way if you allow for branches, because the revisions will just cause branches, rather than change the actual events.

I know you're not going to see things my way, but perhaps others will. That's all I've got to say on this.

[Iscah]

I know you're not going to see things my way, but perhaps others will. That's all I've got to say on this.

Right then, same back at you – I know you're not going to see things my way either, but perhaps other will want to listen to a theory that takes every part of the game and makes it all make sense together, over your theory that chooses to interpret things so they don't make sense with each other.

I came up with my theory to fit Shadowbringers' branching timeline together with Alexander's stable time loops, and then Endwalker came along and I didn't have to adjust anything in my theory at all. That tells me I was on the right track.