@MIRKOSOFT
tokyoracer's right, the C= ones use a microswitches design while the newer A ones a membrane design, at least on the A500.
I don't know what the situation is for A2000 keyboards, but I feel it's similar - C= ones use a different keyboard (with a shorter F-key span, Cherry I think) than the more common Mitsumi ones (which I presume all have the A key).
But it's not impossible that there may be C= key Mitsumi ones, at least for the A2000.