Short answer is that what you are hearing now it is not the same ID that you programmed.
Here in Montreal..take an engine company for example..the engine #225 cab radio would be i801023...but the drivers w/t would be i800563....the capt's w/t could be i800177. And of course the other FF's on that engine also have w/t's with seperate ID's. When thwy talk between each other they would identify "engine 225 driver to engine 225 capt" and so on...but when they talk to dispatch they would just identify themselves as "engine 225" no matter who was transmitting..
The other thing to keep in mind is that a vehicle is taken out of service and replaced by a,spare unit they would identify vocallaly as the unit # they are using the spare vehicle as..they would not use the # that belongs to the the spare vehicle..
Keep in mind the UID you see displayed always belongs the actual radio that is transmitting..NOT the apparatus # that,they say,they are on.
It takes time but you will find a pattern to which UIDs belong to Dispatch...Vehicles and W/T's.
Here vehicles are i80xxxx (i80 & 4 numbers). W/Ts are i800xxx (i800 & 3 numbers)
Hope this helps