You are using a DATE or TIME field rather than a CREATEDATE field. This
field should be put in the original template if possible.
In the document in question, press Alt-F9 to display field codes. Then
change the field to a CREATEDATE field, press F9 and then Alt-F9.
See
http://addbalance.com/word/datefields1.htm for information on the
different kinds of datefields and how to format them.
Nevertheless, the CreateDate field will show the date the document is first
saved on the current system if the field is updated. This is one of the
(many) reasons for not emailing Word documents when you want a static
product at the other end. You can prevent fields from updating by locking
them or unlinking them before you send it out. Still, unless I want the
other person editing the document I send them, I send pdf files instead.