Well if you think about it, PAH must sell a huge volume of hay, so they must have to buy it in from a number of different sources. It could be that the new stuff is a different grass variety, or that it was just harvested at a different time or under different weather conditions.
As long at it doesn't smell musty or dusty and the pigs eat it, it shouldn't be a problem.
I used to buy 150 bales in each autumn for the horses and the quality of what I got would vary from year to year, depending on what the growing season was like and how good the weather was when it was baled.