Just been on the web site and the black 3 is the one that adjusts furthest to the right.
The Black 1 & 2 don't have as much adjustment to the right?
It's not so much the plastic check piece thats different, it's the metal mechanism that holds the cheek piece that is different. The ratchet arm on the 3 is on the left on the 1 & 2 it's on the right when viewed up side down.
Check out Edinkilie web site for more info.
Some how I have two Black 1's which I didn't use.
Hope this helps.