I think it's something to do with knowing about it in the bestiary and surpassing the level of the creature will make them yield less. I'm not 100% on that though.
Here is the link talking about multiple griffins. It actually doesn't specify a number, so sorry about that.
It does specify multiple griffins, and does say that all big monsters have special abilities that you must contend with /except/ for the first griffin, because that fight is about teaching you to deal with a flying enemy.