Mo. Rev. Stat. § 92.865: Amended petition, when allowed.

At the option of the taxing authority or tax bill owner, all claims for land taxes against any parcel of real estate, which has been included in any petition filed under sections 92.700 to 92.920, where such taxes have become due and payable after any tax list or petition thereon has been filed, may be asserted by amended petition or by answer filed before judgment, and, if allowed by the court, shall be included in the judgment against such parcel of real estate.