Does WEP protect message authenticity?
It makes no sense since its nonsense. Let me explain why. Consider an attacker who captures a message of the form $(IV,c)$ for a plaintext $m$ that is not known to the attacker. The aim of the attacker is to "push" the message $m\oplus\Delta$ (e.g., the attacker wishes to flip some bits of $m$. Then, since CRC is linear, the attacker can compute $c'=c \oplus(\Delta,CRC(\Delta))$ and "push" the message $IV,c'$ which will decrypt to $m\oplus\Delta$. 

Technically, one could argue that the text is just arguing that you can't push a message with an unknown IV and here I am reusing the IV. However, who cares if the attacker reuses or not; the recipient will accept reused IVs so the attack works.