As far as I know,BSC sends IMMD Assgn Reject to the MS each time for
1.no available channel
2.channel activation failure
3.channel activation timeout
for each type of access reason.I dont know any such feature in any vendor which prohibits this(except ALU).
Also,you are right,we dont need to count this,as we need to count only SDCCH seizure requests & successful SDCCH seizures to account for SDCCH Blocking.