Even though some might debate what the MSHSAA claims in regards to the individual and team championship accomplishments any given program may have earned over the course of time, they are the source and what they say goes until somebody can prove them wrong beyond a shadow of a doubt.
Just because an individual may have attended an event 20-30 years ago, that won't be enough to sway the governing body for all things prep sports in the state of Missouri. It's up to the MSHSAA to decide what's legitimate and what's not, so unless someone has indisputable video evidence to contradict what the state is saying they're most likely not going to change their mind. Doing so sets a dangerous precedence regarding how the rest of the world approaches them in similar future situations.
For Mexico High School, it does have some previously unmentioned accolades, but only because those events are no longer actively used in competition. Among those are the Mile Relay, in which the Bulldogs won with a time of 3:22.80 and in the Broad Jump current Mexico Assistant Track and Field Coach Austin Miller won in 14.90, one year earlier in 1975 James Clark was victorious in 14.50 and Terry Brooks came out on top in 1979 by clocking in at 14.67.
When it comes to the retired jumps, Hagen was the victor at 21-05.0 in the Broad Jump, Greg Johnson conquered the 440 yard dash in 49.60 in 1976 and in the retired sprints Rodney Henderson claimed the Class 3A 100-yard dash in 1979 in 09.97 and in 1942 it belonged to Hagan with a mark of 10.20 for Mexico.
On quite a separate note, the Bulldogs won about a half-dozen championships for Speech, Debate and Theater, as well, which included Michael Perll in 2012 for Radio Speaking in 1996 J'aime Corrado won for Poetry Reading and in 1979 Janet Brown proved to be a champion in Prose Reading. When it comes to Storytelling in 2000 Jackie Beal made that claim to fame, but she was just following in the footsteps Janna Giger made in 1997.
Yet, both of these players could take a cue from Alan Fisher, who predates all of these accomplishments by having claimed a title in Extemporaneous Speaking in 1977.