Mbox emails missing after import

Hi

I have been having problems with yosemite, and a clean install was needed, so i exported all my mailbox's into mbox format and stored on external harddisk. with the intention to import them again. WHen i have gone to import the Mbox's back, nearly all of hte emails are not visible, where there should be a few hundred there might only be 5 emails. some mboxs dont appear at all.

Please help?