As time goes, everything goes, perhaps, but no duplicates in iTunes! After months and years of use, the pieces have a tendency to duplicate over the ripped CDs or downloaded to the right and left.
There is a simple function in iTunes, which tracks and to clean up the duplicates. Just click on "Music" (or "Movies", or "podcasts" ...) and spinning in "File" then "show duplicate items." Up to you then remove or retain the doubles title!
Clicking the button "Show All" at the bottom of the main iTunes window can return to normal viewing.