Quick note:
It should be remembered that PDF's are capable of being annotated with an overlay which might be a small box or text wihout redrawing the entire diagram.
Depending on the application used to create the update and the software being used to display it, the annotation/overlay may or may not displayed depending on the application of User permissions.
One may want to know whether an overlay had been created for this document. Certain software can also display the date the overlay was added.