There is a privacy option setting that clears out document metadata including the author name on tracked revisions. The location of this setting depends on the version of Word you are using.

See the following link for further info http://wordribbon.tips.net/T010222_M...Anonymous.html for guidance on where to find this in Word 2007 and 2010. I believe that the instructions for Word 2010 also apply to Word 2013.

You can also visit your setting under Word Options > Trust Center > Privacy Options > Remove personal information from file properties on save

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Andrew Lockton
Chrysalis Design, Melbourne Australia