Mo. Rev. Stat. § 206.040
If two or more petitions covering in part the same territory are filed prior to the public hearing upon the petition which is first filed, the petitions shall be consolidated for public hearing, and hearing thereon may be continued to permit the giving of notice of any subsequent petition or petitions. At the public hearing upon the petitions, the petitioners in the petition first filed may move to amend the petition to include any part of the territory described in the subsequent petition or petitions, either as originally filed or as amended. Any such motion shall be allowed by the commissioners of the county commission. The public hearing shall proceed upon the first petition as originally filed or as so amended, and further proceedings upon any other petitions subsequently filed shall be stayed and held in abeyance until the termination of all proceedings upon the first petition, or any petition may be dismissed or withdrawn upon motion of the petitioners therein by their representatives.
§ 206.040, RSMo