When using the course_category_deleted event in an observers.php class, we can not get the previous deleted data from the record snapshot, as this line is missing in the delete_full (course/classes/category.php) core function.

Normally when deleting something which will be used in the observers, the data will be stored temporarily with use of the add_record_snapshot. Afterwards it and can be retrieved within the event observer with the use of get_record_snapshot.