Clause 16.1 clearly differentiates between matters which increase the total of the Prices and matters which increase the Contractor’s total cost. (Notification of a potential increase in Prices is mandatory, while notification of a potential increase in cost appears to be optional-(the use of “may” in the last paragraph of CL16.1).
Why do you think the clause does not include a similar differentiation between matters which could delay the Completion Date and matters which could only delay planned Completion? Particularly when the Contractor is also obliged to submit programmes regularly.
There doesn’t appear to be any sanction in the Contract if the Contractor does not give an early warning of a potential (or even actual) delay to planned Completion?
In my experience the Contractor needs time to consider potential delays that are at his risk before confirming the implications (usually after a programme reschedule) and the mandatory requirement to notify can become an exercise in bureaucracy.