You hold the gun and I'll pull the trigger while wearing a blindfold, then neither of us will be convicted of murder. Won't work. The law is not a computer program. There's this thing called "intent." And "conspiracy", and "guilty as charged", and "punitive fines", and "jail" ...
If C knows (or has good reason to suspect) that the software he got from B is an unauthorized copy then he is contributing to the illegal act, and would likely be liable. It is like "receiving stolen goods" in the non-digital world. Microsoft has "how to recognize an authorized copy of MS Windows" blurbs all over place explaining how their holograms and seals are supposed to look. They do this in part so courts will find it less plausible when someone defends themselves by claiming to have been unaware that some particular copy of Wondows wasn't authorized.
