Due to a misalignment of Key Dates in the Contract Data a Key Date had to be changed. In the process of changing the Key Date as a CE the PM moved the Key Date later in time, with the unfortunate consequence that the Condition applicable to the Key Date (design approval for the relevant section) was later in time than the Sectional Completion Date i.e the section was to be completed before the key date by when the design for the section had to be delivered for approval. Does it follow that a change to the Key Date in these circumstances requires the Sectional Completion Date to be changed to a date later than the Key Date, keeping in mind the change was effected by way of a CE and the provisions of core clause 65.2?
If all of the activities and milestones were logic linked correctly then the programme should have given you that answer. Given that a Key Date is within a section of works with a Sectional Completion Date under X5, it would seem that a delay to planned Key Date would lead to a delay to planned Sectional Completion Date - all of which should be assessed within the original CE that affected the initial Key Date.
A change to Key Date will not always directly affect a Sectional Completion Date - as the Key Date whilst important may not be on the critical path that leads to a Sectional Completion Date - hence the correct logic within the programme when you are assessing any delay should give you the right answer.