A notebook cover lives in a bag with a laptop, a charger, keys and a water bottle. That is the environment it is designed for, and most of what happens to it there is cosmetic.
Here is what is not.
Water in the bag
A leaking bottle is the one thing that will actually change a cover. Vegetable-tanned leather takes water without harm — it dries a shade darker and evens out over weeks — but only if it dries slowly. The damage happens when a soaked cover is then dried fast: on a radiator, in the sun, or with a hairdryer. That stiffens the fibres permanently.
If it gets wet, put it somewhere at room temperature and leave it alone for a day.
Corners
Corners take the most contact of any part of a cover, which is why ours are rounded rather than square: a square corner catches on the inside of a bag and curls. Rounded ones wear evenly.
Because the hide is dyed through with no topcoat, a worn corner shows more leather rather than a pale patch. It gets darker, not shabbier.
The fold
The fold is the only place a cover is under constant stress, and it is the place a coated leather fails: the finish cracks along the crease. Uncoated veg-tan has nothing to crack. It creases, the crease darkens, and it stays.
On a trifold there are two more stress lines, at the fold and at the flap corner. The same applies. On pull-up leather they go paler before they go darker, which is the hide behaving normally rather than wearing out.
Keys
Keys scratch. On Pueblo the mark usually disappears under a thumb because the surface is brushed fibres rather than a polished face. On Buttero it is a visible line for a few weeks and then blends as the panel darkens. On a black or burgundy cover you will not find it at all a month later.
A deep cut through the grain is permanent on any of them. That is the one kind of mark that does not heal.
What actually ends a cover
Nothing we have seen so far, other than heat. The elastic wears out first — which is why a spare cord ships in every box — and the leather outlasts it by years. If you want a cover to last, the whole care routine is: let it dry slowly, keep it off the radiator, and use it.