this is true. But unlike water and salt, it matters very much for ultra-processed animal feed, which does not meet the advertised nutritional values stated very clearly on the bag, after its Best before date.
I was half-way through writing a very long response as to why the BB date is poor in general and a fools errand for chicken feed when I decided that no one would likely read the whole thing and it was wasted effort.
Oversimplified version: The numbers on the feed bag will only be generally true at date of manufacture and there are way too many variables to define a real BB date, so where allowed, it is more accurate to simply state that these are the minimum numbers they deliver and when it was manufactured. The rest is up to the consumer.