Well, something just kept bugging me about the whole business. I can't remember the person's name, but they emailed me privately with additional questions. My first response was that it stands to reason that it was going stale after the bag was openned. Well, the more I thought about it the less that make sense. I asked him what the best way to store hay was, given not having access to a luxurious barn loft.
Plastic draws moisture which causes mold and rot.
Plastic could be a garbage bag or even a trash bin with or without a lid. He said don't use either. Also, if you buy hay from pet stores in those plastic bags, get it out of there into a wooden or cardboard box- something that breathes. Again, this draws moisture causing mold and rot. However, when it is broken open to feed, the center will be just as fresh as when it was baled.