Answered: NEC3 ECC: Assessing a revised CE under option C

The PM's argument is not a valid argument under the contract.
The PM does not have the authority to decide how a compensation event is assessed.
Both the PM and the Contractor must assess the compensation event in accordance with clause  63.1 .This clause confirms that the switch date between actual Defined Cost and forecast Defined Cost is the date of the instruction etc. Further information is also provided in the Guidance Notes