Artist Names not Appearing on iPod

My wife and I have two iPods on the same computer synched to two separate Libraries. We occasionally will purchase music into one of our libraries and later will want to add that file or album to the other library. Initially, we found that we could use "File/Add Folder" or "File/Import" and browse to the other's "iTunes Music" folder on our C-Drive, find the artist name and grab the folder or file. That worked well. Lately though when we try to browse to the other's "iTunes Music" folder on the C-Drive, not all of the artists are listed. Is there a way to fix that?

Is there a better way to transfer individual songs or albums between Libraries on the same computer?

Also, even though we have successfully transfered songs between libraries, when the iPod is syched to the receiving Library, the artist name does not appear when "Music/Aritsts" is selected on the iPod. . . The song does appear in other places, but not under "Artists". Any way to fix that?

Thanks!