Hmm. I've only seen the IPSC-CB. That IPSC-CL is new to me. Is it the course designer to choose which one they run?
Yep.
The "Classic" target (aka the turtle target) was born because some of the IPSC regions can't use targets with simulated heads on them. Because it has no head, it also has no B-zone (which has the same point value as the C-zone anyway).
What I find ironic is that the turtle is actually a better target to represent the more vital part of a human torso than the IPSC metric target, especially if you turn it upside down. I don't know if that was intentional or just a happy coincidence. The classic does present a slightly more significant marksmanship challenge in some ways, since it is less forgiving of lateral deviation than the metric target.