Ah, you're right. I forgot that. Still, if it can't even stop a knife...

Wrong; while certainly bulletproof, Kevlar isn't actually stab proof. Do you know what Kevlar is? It's threads, super-strong, durable, and impact-resistant, but threads, nonetheless. Now, there are variations of the basic armor material that are thicker than others, but the main point is, there is no non-solid armor completely invulnerable to a knife.

While you're right, the basis of the content is Batman Begins, and Lucius clearly says, which is why I put quotes, "This sucka will stop a knife"