Can't play music or see artwork after iTunes redirect

I've just finished moving my iTunes folder from one external drive to another. I then deleted the library on the first drive, but I was not able to delete the Library.itl, Extras.itdb or Genius.itdb. I recovered them from the trash and saved them. I was running iTunes (now redirected) during the deletion. After the deletion, iTunes was still running fine until I closed and reopened it. The media, playlists and play counts are properly listed but the media wasn't located when clicked and there was no artwork. The files are all on the new drive, along with the artwork. I've succeeded in redirecting it such that SOME media now plays and SOME artwork shows, but not most. Oddly, for the albums that don't show artwork on the main icon, they do show it in the "now playing" bar at the top of the screen.

How can I redirect to all the media files and artwork properly? Nothing essential was deleted I know of. (Or presumably connecting to the media would accomplish both?) If it matters, within the iTunes folder I have iTunes Media folder, Album Artwork folder, Previous iTunes Libraries folder, Extras.itdb, Genius.itdb and Library.xml. Inside the iTunes Media folder, there's the Library itl. file. I also was prompted to reorganize the folder to maintain the "Keep iTunes Media folder organized" so I did that.

UPDATE: I think I may have worked out why certain media wasn't playing, but the artwork problem remains and is unrelated. Songs will play, the art will show in the folder as part of the metadata, will show in the top iTunes bar, but not on the main icon in the library. Any ideas about this?

Thanks for any help. Have done this before without any problems.