Some recordings are linked to same work more than once (as recording and as cover recording).
Currently there is 1567 cases.
SQL to find those:
SELECT work.gid as work_gid, recording.gid AS recording_gid
JOIN l_recording_work ON l_recording_work.entity1 = work.id
JOIN recording ON recording.id = l_recording_work.entity0
JOIN link ON link.id = l_recording_work.link
GROUP BY work.gid, recording.gid, link.link_type
HAVING count(l_recording_work.id) > 1