Mo. Rev. Stat. § 138.320

It shall be the duty of the state tax commission to make out and forward to each county clerk, from time to time, for the use of such clerks and other officers, suitable forms and instructions for carrying this chapter into effect; and all such instructions shall be strictly complied with by the officers in the performance of their respective duties, as required by this chapter. The state tax commission shall give its opinion and advice on all questions of doubt as to the true intent and meaning of the provisions of this chapter.