Gonna take a stab at it here.
If you are referring to the no FG initials on the reverse
of the
Kennedy half dollar then that is just die wear/deterioration or debris filled dies. I never heard of a die variety that omitted the FG initials. However some people
do pay a premium for them. That may be their forte. In reality
they are only worth half a buck. Unless they are silver halfs
or higher grade coins or proofs etc.