I see several questions that probably have not been answered and sorry, I was teaching today and just now got time to catch up.
To clarify a bit: A comfort chain will replace most common chains in Picco, .325 and regular size 3/8" chain. What makes comfort chain work is that he back bottom edge of the cutter and opposite tie strap are beveled so that when the cutter bites into the wood it rocks back a little, transmitting less shock, or vibration, back through the bar. If you ever get a chance to run two identical saws side by side, one with C chain and one with the regular chain, the difference is very noticeable.
RS is Rapid Super, or full chisel, in .325, 3/8", and .404, and is now available as RSC in .325 and 3/8". RSC3 is the reduced kickback chain, and it does not have a triple humped tie strap in front of the cutter, it has a single humped drive link in front of the cutter. Regardless of where the reduced kickback feature is, when the chain is pulling chips the hump or bump or whatever is below the cutters and should not interfere with cutting. It is as the chain goes around the nose of the bar that the reduced kickback feature sticks out so if the upper quadrant of the bar does hit some wood, it kicks back with less energy than if the cutter's sharp edge hit. This is why green labeled, reduced kickback chain does not plunge cut very well.
RM is Rapid Micro, or semi chisel, and is now a C chain as well. There was a RM2 reduced kickback chain with the triple hump tiestrap, but that has now evolved into RMC3, which will be better for homeowners since many do not know how to keep RS sharp.
The 3 designation will also show up as a humped drive link on the Picco low profile chain.
Someone said it and they are right, the dealer can stock what they want, and many do not stock PM (Picco Micro) chain, since most of their customers are homeowners and probably should not have it anyway.
So to finally answer Burnham, you can get PMC, Picco Micro Comfort, chain which will not have the reduced kickback feature on it. And there will be a PMC3 that is low kickback.