It's the reverse, there is no m_szShieldAnimExt offset but only m_szAnimExtention, like in HL. m_szAnimExtention is used in DefaultDeploy()/SetAnimation() but also in function related to knife/grenade/pistol (ShieldSecondaryFire, SetPlayerShieldAnim(), ResetPlayerShieldAnim, etc) since there is special animation in player model if you have a shield.