1964 Roosevelt Dime, Wide 'Am' (?)

This item has been sitting in my collection for 45 years or so. The notation attached to it says 'small letters, wide spaced AM; S980p' Is this a recognized variety? The reverse is softly struck, and the obverse exhibits a cup-like effect, with the fields rising to the rim. Since there is a variety number in my annotation I must have attributed it at one time, but no longer have the reference. Any information will be much appreciated.