One thing you have to remember is that Blue 8 is not the primary means of dispatch. Often times, you're hearing the voice dispatch well after the units have actually been alerted.
The MDTs and station tones will alert often long before there is ever anything on Blue 8. I spent a lot of time riding with LACoFD during my paramedic training, and we never really paid any attention to the Blue 8 radio. We'd listen to the TRO when we were away from the squad, and there were times we'd get on scene from quarters before we were ever dispatched on the air. We'd get the "Clank Clank Clank Clank Clank" and the MDT beeps, and just look at the screen to see where we were going,.