(1) A finding of the board of county commissioners in favor of the genuineness and sufficiency of the petition and notice shall be final and conclusive against all persons except the state of Montana upon suit commenced by the attorney general. Any such suit must be commenced within 1 year after the order of the board of county commissioners declaring such district organized as herein provided and not otherwise.
(2) Any proceeding wherein the validity of the incorporation of the district is denied shall be commenced within 3 months from the date of the certificate of incorporation, otherwise said incorporation and the legal existence of said district and all proceedings in respect thereto shall be held to be valid and in every respect legal and incontestable.