How does NEC4 clause 61.4 work?

Clause 61.4 is the Project Manager's decision on an event the Contractor has notified under clause 61.3, and it works in two halves. The first half is the decision. The Project Manager may decide that the Prices, the Completion Date and the Key Dates are not to be changed on four grounds only: the event arises from a fault of the Contractor, it has not happened and is not expected to happen, it has no effect on Defined Cost, Completion or meeting a Key Date, or it is not one of the compensation events stated in the contract. If none of those applies, the Project Manager notifies the Contractor that the event is a compensation event and instructs it to submit a quotation. The reply is due within the period the clause gives. The second half is the consequence of silence. If the Project Manager does not reply within that period, the Contractor may notify the Project Manager of the failure. If the Project Manager still does not reply within the further period the clause gives, the Contractor's notification is treated as acceptance that the event is a compensation event and as an instruction to submit a quotation. What goes wrong is predictable. A reply that says the notification is noted or under review is not a decision, and neither is a refusal on a ground outside the four, such as the budget having no allowance for it. Contractors often fail to send the second notification, so the deemed acceptance is never triggered and the event drifts. And both sides confuse what the deemed acceptance settles: it settles that the event is a compensation event and that a quotation is to be submitted, nothing more. The amount is still assessed under clauses 62 and 63, and the Project Manager can still make its own assessment under clause 64 if the quotation is wrong.