How about modern ammo? If Federal or Winchester ammo is stored safely for 20+ years, will it still perform just as good in 2032?
The short answer is yes.
I have chronographed older LC Match and compared against new loads, the older stuff has greater velocity standard deviations and extreme spreads, but it went bang. I have done the same with old Eley Match, it is evident just from what I can see over the screens is that powder deterioration in the case is real and you can see it in older ammunition.
A longer answer is "depends primarily on storage conditions". The greatest factor is heat. Take a look at table 1 in that UN document, heat ages gunpowder, the more heat, the worse. If the ammunition is kept around 20 C to 30 C, not much change in shelf life, but elevated temperatures due to geography and exposure to sunlight, the ammunition shelf life is dramatically reduced.
The Insensitive Munitions expert I learned this from told me the best storage conditions are unchanging artic. A constant cold temperature and no water in the air.
So the general advice of "keep it cool and keep it dry" is good.
I am ignoring vibration. Per ammunition specialists, ammunition stored in tracked vehicles becomes unreliable if not dangerous. The vibration environment in a tank or personnel carrier is high amplitude and high frequency, simply horrible on everything. I believe it breaks the powder down. But unless you live in an Urban Assault Vehicle, I doubt this will be a concern.