For macOS 10.10 and later only. This applet will scan your iTunes library for pairs of track entries that--very strangely--point to the same file and then copy those tracks to a discrete playlist for further examination; presumably you'll want to remove one of the faux pair tracks without Trashing the single associated file.
This is an issue that is occurring to some iTunes 11/12 users after moving media files from one place to another, perhaps incorrectly.
Progress during the scan.
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View/Edit tags of selected track(s) in single window
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Append the track number of selected tracks to Song Name