Look how different the distance is between the low point of the neck and the edge. Variety? Error? Big head / small head?
Get ahold of a set of Kennedy halves from 1964 to date and really look at them. You will find that the obverse hub design has changed at least five or six times during the run of the series.
Correct. Major changes included lowering the relief of the coin as well as reducing the size of JFK's Profile.
