Guidelines for music videos are still being worked on, so I can’t really give a real answer. YouTube is tricky because thumbnails can be changed for any number of reasons, sometimes there’s a legitimate issue, like correcting a mistake or to update the thumbnail with new info, and sometimes it’s done just to bring more views to old videos, the YouTube algorithm is tricky 
@UltimateRiff might have more knowledge in this field, but me personally I would treat an “old thumbnail” release as withdrawn and replaced with the “new thumbnail” version. But again, not sure if we’re to treat music videos in the same we do regular releases.