To clarify, since it seems a few people are partially lost:
A radio transmitting on a SmartZone trunked radio system like that deployed in Westchester County will transmit (most importantly), in its channel grant request (PTT), the talkgroup number it is requesting and the unique ID of the requesting radio. In Direct Call / I-Call requests, it instead sends the unique ID of the requesting radio and the unique ID of the target radio. In all cases, the unique ID of the requesting radio will be transmitted on a SmartZone system during a channel grant request. The TRS control channel will rebroadcast these in the flow once the grant request is approved, essentially saying "Radio 12345 is starting a transmission for talkgroup 6789 on channel 721".
These radio ID numbers will be in the range from 1 to 65534.
A trunking capable scanner works by picking up this grant message and following the channel assignments as they are given. The same thing goes for private calls in exactly the same manner. Though the control channel might say "Radio 12345 is starting a private call with radio 23456 on channel 721" and only radio 23456 will switch and listen among all the subscribers on the system, the scanner will switch along with it and listen to the call (if so enabled and model capable).
Uniden loves to call direct calls i-calls, and loves to prefix all unit IDs with the lowercase letter 'i' in scanners to differentiate lower-numbered ones from talkgroup IDs. Whether this ID is seen during a group call or private call does not matter: the ID is still the unique radio ID of the currently transmitting radio.
I hope that helps for understanding's sake, and dissipates some of the frustration.