It's a bit weirder than that. It actually does save all the posts, but the "saved" page (like almost every other page on the site) will only show you 1000 items, so there's just no way to access all the older items once they've been "pushed off the end".
I posted some more information about it a while ago here: https://www.reddit.com/r/help/comments/7en0uu/my_saved_posts...
If you unsave a newer one, wouldn't the older one pop up again because it updates the index with limit 1000 again? If the data is there, it should find all posts and then truncate, in that order, if I'm understanding this correctly.
Nope, because the old one's already been pushed off the end of the list and it doesn't re-generate the list when you unsave, just removes the item from the list.
Imagine I have a list of max length 5, when I initially fill it up it looks like [5, 4, 3, 2, 1]. If I save one more thing, it adds 6 at the front, then truncates the list and removes the 1 from the end, so now you have [6, 5, 4, 3, 2]. At that point, if I unsave #3, it just removes it from the list so you'd have [6, 5, 4, 2]. #1 is still saved, but nothing happens to pull it back into the list.
What if you unsave 2 items and save 1. Is then the list remade?
No, the list is never remade. The new item just gets inserted into the list, exactly the same as if it had never reached the limit in the first place.
why would they make the limit so low?
Not sure, the 1000 limit is in the file from its very first version 10 years ago: https://github.com/reddit-archive/reddit/commit/33fd4e9684ca...
1000 probably seemed like a lot at the time or had reasonable performance, and it's just never been changed.
Saving posts is also notoriously unreliable, in my experience. I've had posts where I've clicked the "save" button and it's flipped to "unsave" but upon refreshing the page the button resets as if it was never pressed (and it never gets added.)
Re:How F5Bot Slurps All of Reddit
by bluetidepro on Tuesday July 31, 2018 @08:27AM
(#17652579)
A good work around tip is to set up an https://ifttt.com/ to trigger when you save to offload your saves to somewhere else. I save all my reddit saves to Evernote, personally. It can help with this known issue!
https://www.reddit.com/r/help/comments/6nxqjm/maximum_of_100...