Besed on my govt job experience, I would say CIC works based on FIFO, work is distributed among agents according to some "criteria" that we don't know. Then it all depends on the agent who works on your file (if lazy expect little more delays), keeping in mind that in govt there are more holidays, more sick days (unionize environment, you cant do anything), family time, medical appointment time and December may bring more delays (lot of people going on holiday).
December-March can also speed up things if the overtime money kicks in. ( from unused budget, vacancy savings etc.).
I hope this will help to understand why things are different for the same group of people. (people applied at the same time, some received AOR, some still waiting etc).