With so many
knowledgeable people are
misinterpreting you post , there is a problem.
All that has been said about wrong covers here has been experienced at some time.
of course, GIGO plays some part. A wrong identifier...leads to a wrong cover/(additional) metadata.
If the built in cover finder in the Edit Metadata window is not satisfactory (and you have refined the search configuration for your use).
I also use the Search The Internet Plugin:Find Images (Again, it allows you to update/add other sources)