Mo. Rev. Stat. § 442.430: Title acquired by grantor after conveyance inures to grantee.

Where a grantor, by the terms of his deed, undertakes to convey to the grantee an indefeasible estate in fee simple absolute, and shall not, at the time of such conveyance, have the legal title to the estate sought to be conveyed, but shall afterward acquire it, the legal estate subsequently acquired by him shall immediately pass to the grantee; and such conveyance shall be as effective as though such legal estate had been in the grantor at the time of the conveyance.