You should see the attendant's caller id information during the transfer. For instance, the attendant at extension 1000 has a call to transfer. Once they hit the transfer softkey and dial the destination extension the destination phone will ring and show 'From 1000'. Once the attandant presses the transfer softkey again to release the call the display will change to show the clid of the original caller.
The same thing applies when using the attendant console software.