Yeah printers like the Z2100, Z5200, Z5400 use C ink. Those are basically CMYK printers with some "light" colours added.
The Z3100 and Z3200 use a combo of CMYK and RGB inksets. They dropped the C and use only LC instead (plus the combo of B + GN can make C too).
The Z3100 and Z3200 ink sets are the same except for red, with the Z3200 using the HP 73 "Chromatic Red" instead of the regular HP 70 Red (plus the respective HP 73 vs 70 MK-R printhead).
I often see C ink / heads in bundles on ebay etc aimed at Z3100 / Z3200 printers because the sellers mix them up. I ended up with an MK-C printhead that way.