There's 7 DDO's listed on this site but no photos. Contact John A. Wexler at jwex@comcast.net. https://doubleddie.com/809586.html
It appears like machine doubling as the image to the right is flat in appearance and the one on the left is rounded on the top. There are several names for this , but it is due to the machinery rather than the die itself, so it is of no additional value. All of us has had the same experience when beginning to look so closely. IMO, Jim