If during the consultation described in § 63.2(c), both the agency and the State Historic Preservation Officer agree that a property meets the Criteria, the Federal agency or the State Historic Preservation Officer shall forward to the Keeper of the National Register (a) a letter signed by the agency stating that the agency and the State Historic Preservation Officer agree that the property is eligible for inclusion in the National Register, and (b) a statement signed by the State Historic Preservation Officer that in his opinion the property is eligible for the National Register. Either the letter or the statement must contain substantive information on the property, including a description, specific boundaries, its significance under National Register Criteria, and an explanation of why the property is eligible for listing in the National Register. The Keeper of the National Register shall give written notice of his determination to both the agency and the State Historic Preservation Officer within 10 working days of receipt. If the property has not been accurately identified and evaluated, the Keeper will inform the agency and the State Historic Preservation Officer within 10 working days and will recommend that the agency follow the process set forth at § 63.2. Notwithstanding such recommendation, the Federal agency or the Keeper of the National Register may consider the property eligible for the purpose of obtaining the Advisory Council on Historic Preservation's comments. Documentation concerning properties determined eligible for the National Register shall be kept on file by the agency and the State Historic Preservation Officer.