A couple of things that might help:
1. The MSOffice Clipboard stores the last 24 items that have been copied (from Office documents). Press Ctrl + C twice to open the clipboard and view its contents.
2. If you go to File, Properties, Statistics you can see the total editing time for the document. This might not be accurate if the document is open on someone's machine but they are not actively working on it for a long period.
Cheers
Steve_D