Grading Wheat Cents

I have copied the grading guideline from the coin facts section on this site. I am a little confused since the VF and AU grades contradict each other

G4 Good - Date worn but apparent. Lines in wheat heads missing. Full rims.
VG8 Very Good - Half of lines show in upper wheat heads.
F12 Fine - Wheat lines worn but visible.
VF20 Very Fine - Cheek and jaw bones worn but separated. No worn spots on wheat heads.
EF40 Extremely Fine - Slight wear. All details sharp.
AU50 About Uncirculated - Slight wear on Lincoln's cheek and jaw and on the wheat stalks.
MS60 Uncirculated - No trace of wear. Light blemishes or discoloration.
MS63 Select Uncirculated - No trace of wear. Slight blemishes. Red-Brown color.
MS65 Choice Uncirculated - No trace of wear. Barely noticeable blemishes. Nearly full red color.

If a VF20 has NO worn spots on the wheat heads, but the AU50 has slight wear on the wheat stalks then how does that make sense? Am I reading this wrong?

malissa