Toodledo states they have this on their ToDo list behind several other projects.

I and many others really want this feature.

Then the Toodledo stat reports would actually be useful - I suspect many would purchase this execellent app - I've used thisapp for 2 1/2 years with my Toodledo silver acct & prefer to use this to update the toodledo app - this app is easier and often faster to use.
i see from the vote count this may end up lower on the list - sure would unlock some project tracking and assist with billing for work hours without a manual work around. I use a separate time tracking app because of this missing feature.
Thanks for the excellent app
much appreciated!
--Darl

ability to correct

Toodledo responded that

I am using Ultimate, and love it, AND as Otto said, editing completion date would likely bring others and cement it for me. As it is, I'm here (and looking at other Android todo list programs) to find out if/how to do this.

When I do that, I usually just put the actual completion date in the note field.

This has been also requested on toodledo forum. Simply add field to date form. Mark task completed then edit and edit complete date task. As I recall toodledoSaid is possible via REST api, just needs the UI.

In fact people may purchase your app just to get functionality.