Mo. Rev. Stat. § 579.180: Burden of proof of any exception or exemption upon defendant.

1. It is not necessary for the state to negate any exemption or exception in this chapter or chapter 195 in any complaint, information, indictment, or other pleading or in any trial, hearing, or other proceeding under this chapter or chapter 195. The burden of producing evidence of any exemption or exception is upon the person claiming it.

2. In the absence of proof that a person is the duly authorized holder of an appropriate registration or order form issued under chapter 195, the person is presumed not to be the holder of the registration or form. The burden of producing evidence with respect to the registration or order form is upon such person claiming to be the authorized holder of the registration or form.