1. コミュニティ
2. Product Feedback
3. [Status: Not planned] Editable Task Completion Date

To piggy-back off Rob's suggestion of a using two field to capture the complete date... Another solution would be to make the Complete Date a field that can or cannot be edited based on an Admin se...

1. コミュニティ
2. Product Feedback
3. [Status: Not planned] Editable Task Completion Date

I too would like the ability to edit the Complete date.  Maybe limit it to Administrators to edit that date field so that Users cannot falsify completion.