Bib to authority linking in sample records is messed up
If you look at an authority record, say /cgi-bin/koha/authorities/detail.pl?authid=329 which is the genre Film adaptations, and then follow the link to the 6 records that supposedly use it, edit them so you can see the subfield 9 where the authid is stashed, you'll eventually find the $9 329 on a 710 field for the Library of Congress Copyright Collection, and that sort of mismatch seems to be the norm.
That means if you have a test plan that involves anything around authorities or linking, you need to make step 0 be "run misc/link_bibs_to_authorities.pl and don't worry about that db error when it tries to stuff two 010 fields into one space, just avoid that one invalid record".