I'm not sure I fully understand this purposes stuff, however...
Where is the retention period measured *from*?
If, for example, I set this for a course. Does it get deleted n years after it was created, the end data, last time it was updated, something else?
If, for example, I set this for a user. Do they get deleted n years after their account was created, last logged in, something else?
And so on.... it matters
Other than the retention period. What does the data registry actually *do*. Who sees the results of my efforts filling it in?