How to re-upload songs that have changed to Google Music

Google Music Manager unfortunately lacks such a basic feature as comparing files by their ID3 tag, so if you uploaded music to GM without ID3 tags and later filled them in within the same folder, Music Manager will simply ignore it.

And since I managed to upload about 20 great songs this way, I had to look for a way to get them up there without ending up with duplicates of all the other songs. The first thing I tried was the following, and it seems to work perfectly:

1. Delete the files without an artist in Google Music
2. You have a folder (or folders) on your disk with music for GMusic (mine is GMusic); now create one more (GMusic2).
3. Add the GMusic2 folder to the watched folders in Music Manager
4. Move all files from the other folders (GMusic) into it
5. Click Apply and then OK in Music Manager. This rescans the folders and starts uploading the songs that have not been uploaded yet, which looks like this – as you can see, only roughly the last 20 songs are being uploaded: