Janoshik
That's what everyone uses for this kind of testing. Who knows, maybe you got a good batch. Some say it's from a kind of very acidic cleaning agent the manufacturers use between product A and product B, and some remained behind. Some say it's from sitting around for a very long time (suppliers of raws might have them sitting there for a long time before someone ends up purchasing). One thing it looks like folks can agree on is, it seems like if you brew some up and it's good, you should brew the remainder too, because there's some experience from folks that brewed from the same stash months/years later and it was bad, evident from that PIP.