Once a service provider wanting to avail itself of the safe harbors of 512(b) (system caching), 512(c) (information residing on systems or networks at the direction of users), or 512(d) (information location tools) knows that its system has infringing material, that service provider must expeditiously remove or block access to the allegedly-infringing material. That knowledge can come from a proper notice from the copyright owner, or when the service provider is aware of facts or circumstances from which infringing activity is apparent. It is not necessary for a service provider to police its users, or guess that something may be an infringement.
Sometimes, a notice from a copyright owner falls short of the requirements for a proper notice. That notice does not give the service provider either actual knowledge of the infringement or awareness of facts or circumstances that suggest infringement.
A notification from a copyright owner or from a person authorized to act on behalf of the copyright owner that fails to comply substantially with the provisions of subparagraph (A) shall not be considered under paragraph (1)(A) in determining whether a service provider has actual knowledge or is aware of facts or circumstances from which infringing activity is apparent. {FN89: 17 U.S.C. ?512(c)(3)(B)(i)}
If that were not the rule, then it could be argued that any notification, no matter how insubstantial, would provide knowledge to the service provider of the alleged infringement and require takedown to remain in the safe harbor, thereby gutting the notice requirements. However, a service provider cannot just ignore a faulty notice.
In a case in which the notification that is provided to the service provider?s designated agent fails to comply substantially with all the provisions of subparagraph (A) but substantially complies with clauses (ii), (iii), and (iv) of subparagraph (A), clause (i) of this subparagraph applies only if the service provider promptly attempts to contact the person making the notification or takes other reasonable steps to assist in the receipt of notification that substantially complies with all the provisions of subparagraph (A). {FN90: 17 U.S.C. ?512(c)(3)(B)(ii)}