Display Name and InBox Sorting Order (Outlook 2003)

How come when I get an email from "John Smith" it sometimes appears as "John
Smith" and sometimes as "Smith, John"?

If I send myself a test message, the To: line reads "John Smith
<(E-Mail Removed)>". If I click on the To: name to show the properties, it
shows a Display Name of "John Smith". When I get this email into my inbox,
it then shows a From: address of "Smith, John [WORK.com]", with a From
Display name as "Smith, John".

What is going on here and how can I setup Outlook 2003 to be consistent?

Thanks