Mo. Rev. Stat. § 140.520
No irregularity in the assessment roll, no omission from the same, nor mere irregularity of any kind in any of the proceedings, shall invalidate any such proceeding, or the title conveyed by the tax deed; nor shall any failure of any officer or officers to perform the duties assigned him or them, on the day or within the time specified, work any invalidation of any such proceedings, or of such deed, and no overcharge as to a part of the taxes or costs, nor payment of such taxes or costs, shall invalidate a sale for taxes, except as to part of the real estate sold to the proportion of the whole thereof as such part of the taxes and costs is to the whole amount for which such land was sold. Acts of officers de facto shall be as valid as if they were officers de jure, and if a deed would be valid as to the sale for any one tax, it shall not be impaired by any irregularity, error or defect in the proceedings or sale for any other tax or taxes.
§ 140.520, RSMo