Answered: NEC ECC: What happens when submitting an impact programme the delay is shown but also show critical activities planned to commence earlier?

What you need to be able to do is demonstrate that at the time the CE was instructed (or notified if not off the back of an instruction) show where planned Completion was taking into account progress and any other compensation events that had happened prior to that date. NEC4 now clarifies this in the new 2019 version wording, but is clarifying what the rules always were but now in a more transparent way. If this CE had not come along, you could have been off the job earlier saving money but now this CE means you will have to stay on site longer.

In the same way if you were already running late before this CE came along, and this CE has no further impact then you are not entitled to move Completion Date, where as if you base it on the last Accepted programme it may show entitlement. this same rule would then clearly be in the Employers interest.

So I think what you have said is contractually correct. You need to demonstrate where you were at the point the CE came along i.e. ahead or behind programme, and then assess the extra over impact on the CE at that point. The difficulty you will have is PROVING that you were ahead as you suggest and you are not making that up just to justify entitlement.  

I attach reference to an article here which whilst based on NEC4 is should be the same principle for NEC3:

https://gmhplanning.co.uk/publications/2019-nec4-amendment-to-clause-63-5/