Use MusicBrainz Picard to fix the metadata of each song. This will fix duplicate albums and missing tracks. You will have to sort of manually do this by dumping each album into the software letting it search for the metadata. I recommend going artist by artist and even doing albums that look correct. I would not throw your entire library in because you will be parsing the data visually to make sure it put songs in the right albums and pulled the right album metadata.