The compensation event should at this stage be assessed on its own merits. Whilst the programme duration's might be a starting point as to what is reasonable, the CE should be assessed as to what the Contractor now believes they will be whilst working as efficiently as possible. If the Contractor knows the works will take longer then programmed then they should show that on the programme. That will be for the CE and original activities. If the CE duration affects planned Completion then they will be entitled to assess that impact and Completion Date would move by the same amount (clause 63.3). Obviously any change to the original planned works would be Contractor liability, but programme should be reflecting reality at any point in time.
In your example here it is only the duration extension that is relevant due to the CE that is claimable as the movement in Completion date. If the original duration was 20 days but should realistically have been 30 days, and now the CE will mean that it should be 40 days, the CE should be for a ten day movement in Completion Date not 20 days. The idea of the CE is that it should put the Contractor in a no better or worse off position after the CE has been assessed (+ fee).
If tender duration is known to be wrong then it should not be used to assess a CE - and that is the same if it is a positive or negative difference.
In your example here it is only the duration extension that is relevant due to the CE that is claimable as the movement in Completion date. If the original duration was 20 days but should realistically have been 30 days, and now the CE will mean that it should be 40 days, the CE should be for a ten day movement in Completion Date not 20 days. The idea of the CE is that it should put the Contractor in a no better or worse off position after the CE has been assessed (+ fee).
If tender duration is known to be wrong then it should not be used to assess a CE - and that is the same if it is a positive or negative difference.