Hi Bek
The expected behaviour if you are uploading completions to an existing course is that they will show as RPL
Are you able to upgrade the 12 site to 16 and then backup the course with user data
This will allow you to restore the course or some activities into an existing course or new course - the options to take depend on whether the users or course already exist on the new system.
If the users don't exist on the new system they will be added along with their activity and course completion data
If the users and courses already exist on the new site then it will trickier as duplicate records will exist
Regards