This 1000 years thing is how (at least on paper) the main components of the medium can chemically stay intact and bonded together. You want this as stable as possible since more stability means more resistance to outside forces like moisture and such. Most discs suffering from disc rot today had a number between 5 years (baaaaad) and 200 years (still not great) and are decaying now.

So don’t take things like this too literally.