Below are a couple of posts where this issue seems to be resolved.
https://www-secure.symantec.com/connect/forums/av-defs-showing-date-01011970#comment-2257571
https://www-secure.symantec.com/connect/forums/01011970-virus-definitions#comment-1849161
https://www-secure.symantec.com/connect/forums/defination-date-1970
As Pete mentioned above, this seems to have been resolved in a later version.
http://www.symantec.com/business/support/index?page=content&id=TECH93059
Hope this helps.