If you run ADExport to populate users from your AD and some of the fields doesn't populate, then check your preferences. Maybe these fields are not supposed to be updated by AD.
Another reason can be that these fields cannot be read at all in your AD unless you have proper permissions. In this canse you will see some of the fields populate, but not others.
To find out if this is the case, run ADExport with /v switch to see what fields are actually being read. If you are missing some fields, you need to find out if you have proper permissions.