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.