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CliffordK brings up an interesting point. I don't have a Mexico but I do have a Superissimo about 1983 vintage. It does NOT have dimples in the CS. I don't have a very good picture of the DS CS but it is the same as the NDS. The CS is ovalized. You can see it partly in this pic.
P1000501, on Flickr
Which is not anywhere near the same level of deformation of the OPS.
Here is a NDS pic.
P1000521, on Flickr
Makes me wonder if someone dimpled the CS to accommodate a poor chain line due to the wrong spindle or using a triple, again with the wrong spindle.