Mo. Rev. Stat. § 242.530

Nothing contained in sections 242.510 and 242.520 shall be construed as preventing the board of supervisors and other officers of any drainage district formed prior to April 8, 1905, from proceeding under the act to which this is amendatory, and to that end they may prepare and file revised topographical surveys and plans of drainage for their district, such revised surveys and plans to embrace and use as far as practicable those already made.