Mo. Rev. Stat. § 472.005
This act* shall apply to the estates of persons whose deaths occur on or after January 1, 1981. The procedures herein prescribed shall govern all proceedings in probate then pending, except to the extent that, in the opinion of the court, their application in particular proceedings or parts thereof would not be feasible or would work injustice, in which event the former procedure shall apply. No act done in any proceeding commenced before January 1, 1981, and no accrued right shall be impaired by its provisions. When a right is acquired, extinguished or barred upon the expiration of a prescribed period of time which has commenced to run by the provision of any statute in force before this act* takes effect, such provision shall remain in force and be deemed a part of the probate code with respect to such right except as otherwise provided therein.
§ 472.005, RSMo
Effective 1/1/1981