Omnifocus allows you to view all completed tasks - perhaps you could set up a Perspective for this. Would that give the peace of mind you are looking for do you think?

If you don't trust that ticking off an action as done, always means complete though, how about adding a note in the notes field as you finish the task stating where you filed the insurance document for example? Again using OF functionality, you could date/time stamp entries if you needed that level of assurance or detail.