If a casebook is completely locked but then, a single event is unlocked, site users will be able to enter data in forms related to that event and create new instances of repeating forms within it. 

However, if a casebook is completely locked and a repeating event is unlocked, they'll only be able to interact with the unlocked event instance. 

They won't be able to add additional instances of the repeating event group to the casebook when it's locked. If additional repeating event groups need to be added, the casebook will need to be unlocked.