- determine the 14000 students who completed the activities in 1000-Old,
- enroll these students in the 1000-New,
If course 1000-Old is marked as complete when students complete the required activities, then you can use the Course Completed enrolment plugin to get them into 1000-New - see https://moodle.org/plugins/enrol_coursecompleted
- "manager" complete the 4 activities.
Set the criteria in 1000-New to “Completion of other courses” (specifying 1000-Old) - see https://docs.moodle.org/39/en/Course_completion_settings#Condition:Completion_of_other_courses
Set the criteria in 1000-New to “Date” (eg.tomorrow) - see https://docs.moodle.org/39/en/Course_completion_settings#Condition:_Date. There would be a slight delay before 1000-New is then marked as complete but it’s at least automated the manual completion that you’re currently doing.
Either way, 1000-New will then be marked as complete for the 14000 students.