I think there are a lot of factors that effect the shelf life of jelly. Store bought VS homemade, sealed container VS once it's open, and how you store it being some of them. I don't know about you, but I store my opened jelly in the fridge so it'll last longer. If you go and make a PB&J and it tastes bad, you can go taste your jelly alone. You can look in the jar and go "Huh, jelly isn't supposed to be hairy." I store peanut butter in the pantry. A warm, glorified broom closet, which happens to be a great place for bacteria to spread and feed on sugars like the ones in fruit. If the residue has gone off, you won't have a way of knowing. Maybe it'll effect you, maybe it won't. Either way it seems kinda unsanitary.