The frequency is correct. It is a carryover from decades ago - before the FCC developed the list of PW channels that it currently has in 90.20. Missouri was one of the first adopters of public safety two way radio years and years ago. Your scanner selects the closest possible channel it can. The system has been operating in narrowband since it implemented its repeater, so you may hear some distortion if the signal is somewhat outside the receiver's passband. You might try manually entering 156.685 or 156.6925 to see if those take, as those are closer to the center frequency. You might also try programming the proper frequency with Starrsoft WIN500 software to see if it overrides the radio's internal firmware increments (that may or may not be possible depending on the radio's VCO and synthesizer).