You got lucky with your dealer and the service and parts department warranting all 4 wheels. The dealership most likely did not get covered from MAZDA for all the parts and labor from that claim if they even submitted a claim. They may have done it as a customer courtesy to you? I notice you are from Northern CA I know most of the MAZDA dealership in the Sacramento and surround counties and cities where is your MAZDA dealership you used. They should get an HONORABLE MENTION. Many never report good things about DEALERSHIP experience on forums only the negative which leads many to assume all dealerships are bad. I have read in the last week or so a members on this forum making negative comments generalizing Dealerships mostly on IMHO what they read form past threads and responses from a few other members that had less then what they expected for customer service at a dealership? Yet when we read the independent surveys that are sent out both by the auto manufactures marketing firms to current and past customers they do not indicate the same information often reported on forums.
When I had mine off I found the manufacturing information on the back representing 2 different places of being manufactured. When you go to a MAZDA Dealer or order on line MAZDA you really don't get a choice what country the wheel is manufactured in. This means that the chances of more then a single wheel having cosmetic issues and it going to happen to the rest unless all the wheel where manufactured in the same country, same time index and plant it is not reasonable problem for all them to have the same problem.
Look at the back of your wheels for most all the information. Some of the inspection information can only be seen with the tire off the whee.