Mo. Rev. Stat. § 379.338: Agreement to adhere prohibited, exception.

Members and subscribers of rating or advisory organizations may use the rates, rating systems, underwriting rules or policy forms of such organizations, either consistently or intermittently, but, except as provided in sections 379.331 and 379.336, shall not agree with each other or rating organizations or others to adhere thereto. The fact that two or more admitted insurers, whether or not members or subscribers of a rating or advisory organization, use either consistently or intermittently, the rates or rating systems made or adopted by a rating organization, or the underwriting rules or policy forms prepared by a rating or advisory organization, shall not be sufficient in itself to support a finding that an agreement to so adhere exists, and may be used only for the purpose of supplementing or explaining direct evidence of the existence of any such agreement.