The PM has not valued a CE correctly and has not included assumptions. Officially CE’s cannot be revisited but can this not be addressed under 60.1(8) i.e. changing a decision that has been previously communicated?
In short, no.
Once a compensation event is implemented then that is it, and only an adjudicator would ever be able to change that (but only then by following the rules within the contract). Clause 65.2 confirms that the assessment is not revised if a forecast upon which it is based is later found to have been wrong. You would open the contract up as a very big can of worms if they could always change their minds on agreed events with the benefit of hindsight.
Only Project Manager assumptions issued under clause 61.6 at the time of instructing the quotation are elements that can be revisited after the event is implemented - but even this would be as a separate mini-compensation event and you cant look at the effect of any other changes other than the assumptions.
There is also the fact that you can not decrease the total of the Prices except as stated in the contract and a PM changing his mind on what an implemented CE should have been is not such a reason.