Not sure if this has already been suggested, but I see that calls can be upgraded. For example, a call can come in as a cooking fire which upgrades to a kitchen fire and then to a residential fire.
I thought about how many calls I have been on as a VFF that came in as a structure fire and it has just been smoke inside of a house. One that sticks out to me was a call for 4 cars involved in a crash and it ended up just being someone who backed into someone else's car.
I think a cool addition to the game could be downgrading some missions kind of like how they are upgraded, just backwards. Same thing for EMS calls, maybe a call that came in as a stroke or a heart attack has a chance to be nothing and EMS can clear quicker.
Just a thought.