Missouri's Workers' Compensation Law does contain a notice requirement. Section 287.420 RSMo. states:
"No proceedings for compensation for any accident under this chapter shall be maintained unless written notice of the time, place and nature of the injury, and the name and address of the person injured, has been given to the employer no later than thirty days after the accident, unless the employer was not prejudiced by failure to receive the notice. No proceedings for compensation for any occupational disease or repetitive trauma under this chapter shall be maintained unless written notice of the time, place, and nature of the injury, and the name and address of the person injured, has been given to the employer no later than thirty days after the diagnosis of the condition unless the employee can prove the employer was not prejudiced by failure to receive the notice."
So, the lack of written notice within 30 days can be a defense to any claim. However, a claimant can defeat this defense if he or she can prove that the employer was not prejudiced by lack of written notice. First, if the claimant can prove that the employer had "actual knowledge" of the injury, there is no need for written notice, because the employer could not have been prejudiced. Aramark v. Faulkner, 408 S.W.3d 271, 275 (Mo. App. ED 2013). Second, if the employer does not admit actual knowledge or the claimant doesn’t prove actual knowledge of the injury, the claimant must produce evidence of lack of prejudice." Id.
Lack of prejudice is determined on a case-by-case basis. “The purpose of the notice requirement is (1) to enable the employer to minimize the injury by providing medical diagnosis and treatment, and (2) to facilitate a timely investigation of the facts surrounding the injury.” Hannick v. Kelly Temporary Servs., 855 S.W.2d 497, 499 (Mo.Ct. App. 1993), overruled on other grounds by Hampton v. Big Boy Steel Erection, 121 S.W.3d 220 (Mo. 2003).