Ah! So is that's the trick! So (from my amateur non-programmer's point of view) effectively what's going on is that the game only has to always-remember your level, gear and quest stage progression, and meanwhile every "cell" in the world is a self-contained thing with its own routines that only "activate" when you enter it, and once you exit that cell "what went on" in that cell (the things you did, the interactions that are not directly quest-related) is only remembered for a relatively short time then re-set?
So basically you're travelling around with a "halo" of remembered cell states around you (of your recent movements), and everything else is just a set of routines waiting to be activated?
You are very clever, you Earthlings
Sort of, that's a simplified way of putting it but you have to gist of it. The world, the "levels" in the Creation Engine are split into cells, interior and exterior alike, and the game has different loading states for them, it will actually load a cluster of cells around your present location to process at its highest state. If you kill enemies or move clutter around, stuff like that, the engine will store all those deltas into your save file along with the cell's visit timestamp and keep that data within the limits of its buffer, whatever that is. The persistence isn't in a geographical halo, but literally everywhere you go within the buffer and time limits.
Whatever else you can say about them, Bethesda has this routine down to a fine art, both in terms of object hierarchies and the buffer limitations. Take Fallout 4, if you shoot some bad guys over in Lexington then fast travel all the way to Quincy and come right back, you'll find everything how you left it. But if you go on a tour down around Diamond City and downtown Boston and come back a few days later, the cell will have reset to its default state. Everything is properly serialised for saving and all the expiration dates make decent sense contextualised in the moment-to-moment narrative, Bethesda know when it's "okay" to discard your impact because you've moved on.
Now consider Cyberpunk 2077 as a counterexample. For instance, I shot two dudes in the Columbarium (?) and decided to throw their corpses down the hill outside, but when I came back for the second one, he was already gone because the space had immediately reset upon leaving it. On the other hand, in another quest I tazed the chick that was stalking Blue Moon, but even after 50 hours of gameplay she's still writhing on that bridge where I left her. Red Engine just hasn't been developed for this sort of open world persistence and can't support that kind of experience, it's got very little "memory" and is almost entirely reliant on runtime generation. Which is also reflected in the saves, its pissant 8 MB files with their blistering 5-second loads versus Fo4's 20-30 MB ones.
It's not quite the issue I am making it out to be. But it has been an issue mostly for consoles in the past. Starting Fallout 4 save file (individual saves) is around 4.5 MB. If you were to do a full playthrough you could end up with an individual save file size of around 30 MB. Much large than just about any other game that does local save file saves.
Personally, I'm not too worried about that, literal decades of playing at this game means that what Bethesda do well, they do very well, and their world state management is some of the best in the business. My gripe with Todd Inc. is that they're too comfortable with what they've traditionally
not done well, stuff like writing and interfaces. I'll bet you a dancing donut that you still won't be able to crouch your way under a Starfield staircase.
I am curious though, what do you mean about "location discovery" that balloons the save file, what data goes into that?