A written order under the hand of an officer empowered to make loans under this Act granting a loan to, or with the consent of, a person mentioned therein, for the purpose of carrying out a work described therein, for the benefit of land specified therein, shall, for the purposes of this Act, be conclusive evidence--
         (a) that the work described is an improvement within the meaning of this Act;
         (b) that the person mentioned had at the date of the order a right to make such an improvement; and
         (c) that the improvement is one benefiting the land specified.