I've attached four screen grabs of three different Kennedy Halves, one 1965 and two from 1967. These are all examples of machine doubling, mechanical doubling, worthless mechanical doubling, or whatever you would like to call it. In the second picture the stars briefly piqued my interest...I hadn't seen the stars doubled before. If you're looking at the names of the files, I screwed them up and am too lazy to correct them before posting.
You are correct about them . This type doubling does not have any extra value. I have seen sellers on the net trying to sell MD coins and listing them as mechanical doubling errors. this is bad
I'd say that if you're identifying MD like this, (a) you're examining the coins closely enough and (b) you've been paying attention. If you do come across a variety that carries a premium, you probably won't miss it.
Standard MD but you can place them in the NAV category. No Added Value Doubling sounds better than worthless and they are not worthless as they can be spent at face value.