[Koha] DB errors during upgrade from 3.18.09 to 3.20.04

[Doug Kingston]

While doing a upgrade on our test koha instance (based on a copy of
production), I received the following errors.:

   - [Sat Oct 24 23:52:23 2015] updatedatabase.pl: C4::Installer::load_sql
   returned the following errors while attempting to load
   /home/koha/koha-test/intranet/cgi-bin/installer/data/mysql/atomicupdate/hourlyloans.sql:
   - [Sat Oct 24 23:52:23 2015] updatedatabase.pl: ERROR 1060 (42S21) at
   line 1: Duplicate column name 'lengthunit'
   - [Sat Oct 24 23:52:23 2015] updatedatabase.pl: C4::Installer::load_sql
   returned the following errors while attempting to load
   /home/koha/koha-test/intranet/cgi-bin/installer/data/mysql/atomicupdate/oai_sets.sql:
   - [Sat Oct 24 23:52:23 2015] updatedatabase.pl: ERROR 1062 (23000) at
   line 35: Duplicate entry 'OAI-PMH:AutoUpdateSets' for key 'PRIMARY'

I know from previous experience that these kinds of error are sometimes
benign, but I would like some feedback on whether I need to take any kind
of action in this particular case.

Thanks,
  -Doug-