Missouri requires UM but not UIM, and leaves stacking to the courts
Missouri's rules are in RSMo 379.203 (UM required), 379.204 (excess underinsured coverage) and 303.190 (minimum limits). The deadline is in 516.120.
Read how stacked and single-limit coverage differ in Missouri, check what the statutes say and leave to the courts, or see how Missouri UM and UIM differ.