Because the master category list is personal to each user. See http://www.slipstick.com/outlook/olcat.htm

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Sue Mosher, Outlook MVP
Author of Configuring Microsoft Outlook 2003
http://www.turtleflock.com/olconfig/index.htm
and Microsoft Outlook Programming - Jumpstart for
Administrators, Power Users, and Developers
http://www.outlookcode.com/jumpstart.aspx
> In our public contact folder we have different categories we file people
> under. Our supervisor created a category and it is not showing on all
> systems, why would that be? How can we correct this? Any suggestions would be
> greatly appreciated.