The ghosted loop Ball Mason jars are a transitional "error". While not truly an error they mark the changeover from the three loop Ball to the two loop Ball molds. They are not common with the quarts easiest to find followed by the half gallon and the rarest is the pint. The third loop can be easy to see or take a sharp eye to spot.
I found this pint over the weekend and thought I would share it with everyone here. As you can see Ball and the underscore have been recut and the third loop left to fade away.