nice looking proof, don't think it is a dropped letter - they are incuse on the coin, this looks raised. Could be a gouge on the die.
But to be certain if it is actually raised or incuse, we need to know where the light is coming in from? If mostly from the E and slightly N, then it is possible the this anomaly is incused. Hard to tell - I guess I'm on the fence until the light source is verified.