If the Project Manager has accepted and implemented a Compensation Event which the Employer has subsequently paid out on is the Employer then estopped (personally barred) from claiming the Compensation Event is not valid should it become the subject of adjudication with regards its implemented value? Please note in this instance the Contractor had placed his dissatisfaction with the assessed amount on record at the time the Compensation Event was implemented.
No this is not correct, the Adjudicator has the power to review and revise any action or inaction of the Project Manager or Supervisor. In NEC3 they could also alter a quotation has been treated as accepted and in NEC4 this power was widened to being able to alter a matter which has been treated as accepted or correct.
The fact that the Contractor stated they were dissatisfied with the assessment is neither here nor there, the only way to dispute it in NEC3 is adjudication and in NEC4 there is the additional right to escalate to Senior Representatives.