With contractual communications it is good practice to refer to the relevant clause under which you are communicating, failure to do so risks the communication being found to be ineffective.
An early warning notification is communicated under clause 16.1 and this should be separate from any other notification so you need another notification communicated under clause 64.4 to notify the PM that they did not assess a CE within the time allowed. This notification is a condition precedent so no notification = no deemed acceptance.