The tapes are "Imported" because they were not created by this install of BackupExec
There is no way that an inventory, followed by a catalog will affect the data on the tape. What is the exact error/warning that you receive?
Rather than catalog every tape, you can inventory/catalog the latest tape that you have, then restore the U01 files in the ..\Veritas\BackupExec\Nt directory, and then see http://seer.support.veritas.com/docs/272886.htm to force BackupExec to re-index and thus recognize all the "imported" catalogs