Yeah, I knew I failed the check the second I made it. I only needed a 13 assuming it hadn't advanced in hit dice. I guess, in the future, you could grant a small bonus for things that should be commonly known. But at this point, I can't really do much about it. Once I get some gold, I'd like to buy a few masterwork tools of knowledge. One for arcana, nature, dungeoneering, and the planes if we start finding outsiders.