Partial items "disappeared" on employees calendar

Hi! I use Exchange 2003, with Outlook 2003 for our clients.  One of my employees swears they had more items on their calendar and that sometime during the day most of the item disappeared but not everything.

I check the basics on auto archive which was turned off as well as another other possible calendars created.

Each night I do a full backup too of the exchange server, is it possible to retrieve one persons calendar from exchange from a backup if needed?

Thank you so much,
James