Sounds like your cassette is a mix of Exa Drive and pre-Exa Drive sprockets.
The "c" in a diamond indicates where the thinner spline is on Exa Drive sprockets; these sprockets will say, for example, "12A" or "12B": the letter indicating which sprockets can be combined together in a cassette.
The pre-Exa Drive sprockets just state "12" or "13" and have the letters "A" to "H" written above the splines, which are all the same size.
Exa Drive sprockets can be used on pre-Exa Drive freehubs, but pre-Exa Drive sprockets can only be used on pre-Exa Drive freehubs.This page has more info.
So does this mean that exa drive sprockets with the A suffix can only be used with other exa drive sprockets with the A suffix and not with B or C suffix sprockets or is it for orientation only?