The deemed acceptance only kicks in if the Contractor notifies that the Project Manager has not made their own assessment within the timescale. If the Contractor fails to notify then the deemed acceptance never applies. If they remind after 16 weeks that the Project Manager has not responded, it will still be a further two weeks before the original quote would be deemed accepted.
If the Contractor has notified that the PM has not made the assessment I do not think you can unilaterally resort to 13.4, especially when it is quite late in the day to make such a statement. Otherwise this would always be a get out of jail free card for the Project Manager in every situation. The contract is all about transparency and timely information.
Time for both Parties to sit around a table and review this matter together and come up with some kind of agreement as to what the value of this event should be - rather than both sitting in different camps waiting for the other to make their move. Following the contract should not be a game for the other to take advantage of.