iTunes Links to a Duplicate of Every Song in Music Folder

I hope someone has a solution for this. Duplicates of every song have appeared in the Music folder on my PC. These duplicates do NOT appear in the list of songs in iTunes itself, but only in the Music folder. The duplicates are named "[song name] 1." Example: Original file is named "Paperback Writer"; the duplicate is named "Paperback Writer 1". When I click on Paperback Writer in iTunes, it plays fine--but it's connected to the duplicate of the song--Paperback Writer 1. I can delete the version with "1" from the album's folder, click to play the song in iTunes, and it requires me to locate the song and select it before it will play. I can't manually re-associate 14,000 songs, so I'm hoping someone has some idea for how to mass re-associate iTunes to the correct songs so I can then delete the duplicates named "1".

I think this may have been caused by an attempt a couple of years ago to revert to an old music library in iTunes when there was some problem I can't recall. After selecting an old library, I think syncing to iCloud was turned on, and it downloaded duplicates of everything, naming the dupes with the "1" extension. But, I cleaned all that up at the time by deleting and re-associating to the correct song files. Now I have a new PC, and in adding the music library to it, once again I suddenly have the duplicates problem again. Any advice is appreciated.