A claim which either matured or was acquired by the pleader after serving his pleading may, with the permission of the court, be presented as a counterclaim by supplemental pleading.
Mo. Rev. Stat. § 509.440
When claim may be presented as counterclaim by supplemental pleading
Effective: 28 Aug 1943; (L. 1943 p. 353 § 75)
Official source: Missouri Revisor of Statutes. Reproduced from public-domain Missouri statutes; confirm against the official source for the current text. Not legal advice.