Yes you are correct. You should have an equivalent "planned Key Date" milestone like you would have a planned Completion, and it is treated exactly the same way when you assess a CE according to clause 63.1 i.e. if it is agreed a CE moves planned Key Date, then Key Date should move by same amount once the CE is implemented.
If your updates show an increase in gap between planned Key Date and Key Date then that increases the terminal float which you the Contractor own.
If your updates show an increase in gap between planned Key Date and Key Date then that increases the terminal float which you the Contractor own.