If you compare the nickel with the missing crossbar on the "E" to a regular proof 1961 Jefferson nickel, the thickness of the lettering is significantly different. Might the less pronounced (or slim nature) thickness of the lettering be evidence of a weakly hubbed die, which was weak enough that the crossbar was not created in the die? Also Searching around I found that someone has found a 1960 proof Jefferson nickel with this same flawed "E".






























