Seeing no replies with your questions I suggest you contact the Tech Advisor for your year car. Either he or someone that participates in judging may have the answer. 

@captain1562-2 Daniel, I have no specific knowledge of your specific question about the 1940/41 wheel rings. But here are my thoughts on your question, in a general sense.

Stamping dies are made in sets of two so that when they come together with the part between them, they produce the desired pattern. My theory is, that as the dies are used over and over, they start to wear. As the wear progresses, the features of the resulting parts would become "softer' or not as crisp as when the dies were new. Sets of wheel rings would be made up as the parts were produced, so there would never be any noticeable difference between the individual pieces of a set.

After finding significant differences in the ribs on truck running boards. I came up with this B.S. theory to explain it. It would be equally true, or equally B.S. for most any stamped part.

Mike

@35mike Mike, thanks for your response! That makes a lot of sense. That would explain why i always see 3 that match and 1 that is different.

@captain1562-2 Like Mike, I can only speak in general terms but Mike is correct about wear on the dies. Stamping dies (nearly all production tooling actually) have a finite number of uses before they become out of spec and have to be reworked or replaced. Each stamping reduces the "crispness" of edges a tiny bit. Whether they were made in sets to enhance conformity I have no clue but it makes sense.

@tiny thanks Tiny! That makes the most sense.