This is why there is a contractual requirement to show a "planned Completion" and a "Completion Date" milestone separately. The Contractor shows where they plan to finish, compared to contractually when they have to finish to avoid paying delay damages. A Completion Date can only be moved with an implemented compensation event. It sounds like your first two compensation events agreed that planned Completion had moved by two weeks so therefore Completion Date was entitled to be moved by two weeks.
Any further lack of progress by Contractor should show planned Completion moving, but with no entitlement to move Completion Date if this is not due to the effects of a compensation event.
Any further lack of progress by Contractor should show planned Completion moving, but with no entitlement to move Completion Date if this is not due to the effects of a compensation event.