As an admin, you can always modify those dates. I'm not recommending it, but it is possible--If you use adminer, you can hunt down specific sessions and bulk change the completion dates and go to the course completion status and bulk change the completion date there, too. Again...not advocating, just saying...
Face-to-face (plugin)
Can I use Face-to-Face to create an event in the past
This discussion has been locked so you can no longer reply to it.