Station M et al
It's not unheard of one town, station, department etc, dispatching for another on a non-routine basis. It could be for one of a number of reasons, announced or unnannounced. Some of the most "common" are
Equipment breakdown
Equipment changeover
test purposes
personnel shortage
interop verification/exercise
Some instances are rare, some not so rare. I wouldn't get too concerned when "Station X" shows up dispatching for "Station A"
73 and good listening
Mike KM1R