Aside from the primers the "quality" needed for long shelf life is in the alloy and annealing of the brass and the quality of the chemical makeup of the powder. Neither of which can be seen or measured, other than by examining how they endure over time.
One of the main components of smokeless powder is nitric acid. Done just right in production, the powder will remain stable for multiple decades. Done less than "just right" and the powder can chemically break down over time, releasing nitric fumes which also attack the brass of the case.
Storage conditions WILL affect this, as well.
The Military has a set "self life" not because ammo will go bad after XX years, but because it MIGHT. Some things have a shelf life, then get tested and "reset".
I ate Korean War C-rations (52-53) in the 70s. C-rats were good for 7 years. Then, they pull one case from the stored lot, check it, and if its still good, the entire lot is good for another 7 years. repeat until used up...
Was bummed when we got the "modern" (Viet Nam era) C-rats. The new ones didn't have smokes in them!