Mo. Rev. Stat. § 369.164: Attorney in fact, association may recognize, when.

An association may continue to recognize the written authority of an attorney in fact to make any addition to and withdrawal from the account of an owner until it receives written notice of the death or adjudication of disability or incapacity of the owner, or of revocation of the attorney's authority. Any payment by the association to an attorney in fact prior to receipt of such notice shall be a complete discharge of the association as to the amount so paid.