what i meant was that a Channel Request message does not contain any information about the BSIC. When a MS sends a Channel Request on a certain frequency, all cells using this frequency as a BCCH can hear and decode it.
They will understand it as a valid Channel Request, whichever their BSIC.
The only constraint is that it’s on their BCCH frequency, and it reaches the BTS during the TS0. If it arrives after or before, it’s going to interfere another timeslot of the TRX.