Do you need to go over 100% to finish creatures?
See screen shot below. I am at 100% still shows not completed. AKA after it showed 100% I had to kill one more in order for last skill to unlock.
Some of the creatures are going over 100%.
Wisps if I remember right go to 103% currently.
Skeletal Knights and Skeletal Warriors also go over 100%.
I don't remember the others I'd have to check my knowledge book
I want to add to this that I was just killing goblins and watching the knowledge gain after every kill. Goblin Enforcer unlocks Enrage at 60%, but there's no indication like a message on screen or the arrows when you open the book until the next kill at 63%.