The guide Larry linked to is old and outdated. The checks and X marks mean nothing, the arrows show a placement or space in the coo to determine which coo it is. It is not a good guide to use as reference anymore so we suggest either using this one:
Which is one that was created by a person named Wolff who did the earlier outdated one also
The black is customized, not relevant to a variant. The purpleish limb color is degradation in the plastic. I don't have the time to look them over closer at the moment, but I would think they are all Kenner figures with varying degrees of degradation. Also different factories used different plastic and plastic mixes so some have soft limbs, harder limbs, hard or softer torsos, etc... These can be used to determine certain variants such as the pbp stormtrooper has a hard torso, but in and of themselves is not a determining factor. For the figure to be considered a certain variant it must meet all criteria set fourth for the variant, in example of the pbp it must have the certain coo marks established to belong to that group, as well as the harder torso, the softer limbs, the whatever. I will look at these closer tommorow, but for now two coo guides should get you started to at least determine which coo family they come from to even see if they can be non Kenner classification.