Now I am not sure where I read this, but to my understanding, the machine that put the numbers on the casting rolled it on, so one could conclude if moving L. to Rt., pressure would be exerted down and also in a Rt. direction. When the pressure of the roller got to the end of the die more pressure was concentrated on less surface area resulting in the end letters, "A"&"G", being deeper and more pronounced and you can see in the pics the right side of the letters are elongated to the righthand direction showing the force of die roller. I also theorize that some characters (numbers-letters) were fixed in the die meaning bolted in so they did not need to be changed as often. I say this because many stampings are heavier where the "837" is as opposed to the "1100" . I believe that the 1100 was one set of "fixed" dies and the 837 was in another gang holder that could easily be swapped out. Don't beat me up, it is just my theory based on observation, facts and what makes sense in production as I have an Aerospace machining background. Once the die was set up with the redundant information (everything except the date and the 837 or whatever last 3 numbers used), they would be shelved until needed and the rest of the data added explaining different boldness of characters. I should add the same pressure to surface applies to the far Left characters as well. Also casting tolerances diameter and out of roundness affect clarity and depth of characters.