Have you tried "RIGHT CLICKING" on the file in Windows Explorer?
In Windows NT you could into the Ownership tab and it should display the last person to save the drawing.
In Windows 2000, you need to go into Advance to see the owner's name.
It makes sense that anyone who last saved the file would be the last to edit the file, unless they opened it and saved it after just plotting or taking a peek.
Just a thought.