The documents whose date changes have a DATE or TIME field instead of date
text or a CREATEDATE field. If the template on which the documents are based
contains a CreateDate field, this will always be correct in the documents.
For the existing documents that contain DATE or TIME fields, press Alt+F9 to
view the field code, change DATE or TIME to CREATEDATE, then Alt+F9 to
toggle the view back to field results and F9 to update. For more, see
http://word.mvps.org/FAQs/TblsFldsFms/DateFields.htm