Interesting to note that there are some things that Locution does that the average radio listener doesn't pick up on.
For example, the locution house overhead speakers in each station are usually NOT fed by the radio. Instead, they sound immediately when the station is tripped. So, even if there is another call being dispatched on the radio, the house overhead will announce the call before it's heard on the radio. The radio dispatch message will go in the queue, and will transmit itself as soon as the previous message is finished. Which is why you may hear two or three dispatches for Seattle run one right after another on 4A, then on the Ops channel, you hear the apparatus responding before the locution is finished. Of course, the rip and run printers are also a tip off, as they start printing usually before the house overheads trip.
(The "zzzzzzz...zzzzzzzz...zzzzzzzzz" of the dot matrix printer is like an instant alarm clock.)