NEC3 ECC Option B
The PM provides an assumption for a compensation event (61.6), the assumption being that Others will carry out their work by a certain date. The compensation event is implemented and the Completion Date is extended by x weeks as planned completion is delayed. The Others complete their works earlier than the assumption, the PM issues a compensation event (60.1(17)) to correct the assumption which results in a negative value, as planned completion is x weeks earlier. The Completion Date cannot move earlier, therefore the Contractor retains the benefit of the later Completion Date without prelim recovery. Is the application of the assumption provisions correct in this scenario?
When you say that the PM assumed they would carry out work by a certain date - is that what the assumption was? The exact wording will matter here. If it was ‘this work by an Other will be completed by 31st March’ and the actual completion was 25th March, then the assumption is correct and there is no CE. If the assumption was ‘they will complete the work on 31st March’ then its a different outcome.
Assuming you have actually passed that hurdle, and given that planned Completion will be earlier as a result, then yes, you have a -ve compensation event. That would include both ‘direct’ and prelim costs. You are right that if the Completion Date went out, it can’t come back. However, the cost of the time (i.e. Prelims) can be reclaimed.
Your terminal float will increase, so the Contractor is still benefitting.
Thanks @Andy.ATNEC, noted your point on wording - it is ‘complete’!