Any valid compensation event when it is quoted/assessed will assess the impact of that event upon any relevant Key Dates or Sectional Completion Dates, as well as overall Completion Date (or more specifically the planned date, which then allows the Completion Date to be moved by the same amount).
Sectional Completions are not necessarily linked to the Completion Date, but a correctly logic linked programme should give you the correct answer when you impact the CE into the programme and reschedule it. If it moves the planned Sectional Completion Date, then there is an entitlement to move the Sectional Completion. If it also moves planned Completion, then Completion Date should also move, but if it doesn’t then it is only the Sectional Completion that is entitled to be moved.
Even if it is linked, they are obliged to mitigate the effects of a CE (mitigation being at no additional cost or risk) so if they CAN re-sequence to maintain the Completion Date then they should. Note however that you can not impose acceleration - that has to be by agreement.