MS Outlook Problem

I formatted my clients system but befor that i took a back up of his MS Outlook mails and archives folder and also did manual copy of pst files to other drive after formating system when i imported mail and achive file found that inbox mail were available till 6months and all older mail were not showing.

Even i tried with manual copied pst file but it was same pls help how can i retrive his mails i know i copied whole his outlook folder

Pls help me