Files Renamed in Finder not Reflected in iTunes?

Unfortunately, updating the files in Finder will not update the files in iTunes. This is because iTunes uses a file called iTunes Library.itl as a database of all your media.

You can however use the automator actions "Get Specified iTunes Items" and "Set Info of iTunes Songs" to automat the process of updating the metadata. There are some other good Automator actions in there too.

What's worse is that by doing this, iTunes has no idea where the renamed files went. The key to any iTunes-related file management is to do it within iTunes itself. If you choose File -> Library -> Organize, then "consolidate" the library, you will see a large number of exclamation marks next to the renamed files. If you don't re-attach iTunes with them, it will not be able to play those files, sync them, etc.

The simplest solution would likely be to restore from backup (or otherwise undo the batch change) then re-write your AppleScript to talk to iTunes instead of Finder.

You will need to clear all the songs in your library then drag the media library folder into iTunes,

This will reset all the files into iTunes as by renaming the source files you would have broken the links between the software and the music file.

When ID3 are missing, it would be very easy for iTunes to read the file name and use that as its track name in ID3 but if there is no ID3 tags on a file it was obviously not purchased from any music store so as far as Apple is concerned it is not a file worth caring about...