restored my ipod - artists were simply not listed under "Artists"

I restored my ipod today due to the fact four or five artists were simply not listed under the 'Artists' category upon my ipod - in spite of being listed under albums and being apparent were I to view my ipod through itunes. I tried fiddling with their names/categories through itunes in the hope that would amend the issue after restoring and rebuilding my ipod, which it did not. Can anyone perhaps suggest a resolution if this is a known issue?

The artists affected were: Charles Mingus, Malachi Thompson, Nina Simone, The Imagined Village and Billie Holiday. Each only had the artist field filled whenever I selected 'Get Info' so I tried to fill in the Album and Album/Artist fields to resolve the issue, but to no avail. Would anyone happen to know what is happening? the artists are definitely upon my ipod and named correctly - but they shall only appear under music>albums rather than music>artists.