All great advice that I follow assiduously. I don't want to waste precious money on spoilt feed! And I don't allow any moisture in my feed room at all. If something is wet from a ride it has to dry out before it's allowed back in.
I'm glad they qualified the "use by" idea. We own a feed a store and the problem with the "use with 45 days of purchase" is that it's not really relevant. If you buy from a store that carries a lot of feeds, it might be that some of those don't move quickly. We only carry two manufacturers and there isn't a bag of feed that sits here more than a month. In fact, many don't make it a week. Having said that, realize that if you buy a specialty feed and if it's the last bag on the pallet, it MIGHT have been there for quite a while. Some mills don't put dates on their products so you just have to either know what moves or ensure their is an exchange policy with your store.