Hi Pete

I had a look through the tracker for issues fixed in version 9 around course completion and couldn't find any.

Its my understanding that changing any activity completion condition means that the course completion will be recalculated based on the date that the condition was changed. 

There is an option to either keep the existing course completion records based on the previous course conditions in which case the old date would remain 

or delete the existing completions and recalculate based on the new conditions in which case the date would be the date when the condition was changed and the completion condition was met.

It sounds like the Unlock without deletion option may have been chosen for this