single track on disk showing as multiple iTunes entries, how to clean it up? If I 'show in finder' on the "duplicate" then both entries in iTunes point to the same track, how do I clean this up, preferably for the entire library as I've seen a few instances of this
Go to View → Show Duplicate Items. Then, sort the list by date added and remove the most recently added duplicates so the originals remain.

For more information on removing duplicates, see the Apple KB article:


How to find and remove duplicate items in your iTunes library