Have been in this forum for a while so I recalled something like this was discussed previously: post #3318. But of cos nobody knows if this is true unless u have worked in MOE HR i guess?
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HR will flag officers for promotion at intervals. The algorithm that determines this interval is not known to us, all we know is that it is somewhat related to CEP. Based on this, the school then decides whether to support/not support the promotion. HR will then execute the final decision.

That's why they say that "the rate at which you MAY be promoted depends on CEP, but whether you are actually promoted at each instance depends on your performance". You would have heard this line while in NIE before, or even from colleagues/mentors.