I upgraded to Office 2013 recently. I recreated my outlook profile to make sure that I have a clean environment. I notice several emails that are missing the sent date. In outlook.com they appear correctly with the sent/received date; In Outlook 2013 however, in the list view they show with today's date, and when opening the email they show "None" for the date.
I also noticed a few that are missing the sender name and recipient name, but the missing date seems to be the most frequent.