Outlook 2000 Restore

I have a user who had to reload Windows 2000 on his PC. Before the reload we backed up everything to a CD, including outlook.pst and archive.pst. Once everything was reloaded he tried to restore his outlook files from the CD. Everything after March 2002 was lost. Is there anyway to recover the emails that were after that date? We had searched the hard drive for all .pst files and there was only the 2 we backed up. How could there not be anything after March 2002?