Zooker, controllerzhu, With respect, I think you are missing the point of an anonymous ’Blocked’. Pilots can often hear radio exchanges which are lost to the controller.
An example; you issue a climb clearance to ABC. However, DEF had misheard the call-sign and thought it was for him. ABC and DEF reply at the same time. ABC, the correct respondent, is closer to your receiving antenna and his call completely obscures the incorrect call from DEF, and both commence a climb. Now you’ve got an aircraft going walkabout.
However, it’s just possible that a third aircraft was in a position to hear the radio conflict which you’d missed. An immediate ‘Blocked’ could well alert ABC/DEF to confirm what they are/aren't supposed to be doing.