[Blatchara]

I know this works in context view. Choose which context(s) you want, then select "Completed", and ask it to group by "Completed". You will then get the lovely outline of tasks completed today, last week, and last month.
If you get something older than "last month" for this view, let us know what "pre-alpha" software you were using...
I did try the same trick in project view, and it doesn't work the same way. Maybe that's an as-yet unimplemented feature. It really should work the same way that it does in the context view.