POD says: =item B<-d, --delete> Delete EVERYTHING related to biblio in koha-DB before import. Tables: biblio, biblioitems, items What happens if you combine this with --authorities? One interpretation could be that nothing will happen. Another could be that you delete all biblios, even if you are importing authorities. The code looks like this: if ($delete) { if ($biblios) { print "Deleting biblios\n"; $dbh->do("DELETE FROM biblio"); $dbh->do("ALTER TABLE biblio AUTO_INCREMENT = 1"); $dbh->do("DELETE FROM biblioitems"); $dbh->do("ALTER TABLE biblioitems AUTO_INCREMENT = 1"); $dbh->do("DELETE FROM items"); $dbh->do("ALTER TABLE items AUTO_INCREMENT = 1"); } else { print "Deleting authorities\n"; $dbh->do("truncate auth_header"); } $dbh->do("truncate zebraqueue"); } So it should do the right thing. The POD should say that --delete --authorities will clean out the auth_header table.