On the subject of Anderson the cheater. There are definitely way more cheaters than the two we know of (the other being MC), but these two Bella caught and Philip confirmed. So they took tests those two were in charge of. Cathy was no doubt in charge of more classes than the two gen ed ones and it's possible that Philip took over all the math ones and Bella all the English ones and Philip naturally had other classes on top of that, but we should still consider the gen ed students to be the primary suspects. I'm going to have to reread the relevant ep 10 dialogue and see if Bella and Philip are specifically talking about the gen ed tests.
The point though is this: If Sally didn't take classes that Philip and Bella were in charge of, she can't be Anderson. Cheater she may still turn out to be, but not the one who was caught.
At the moment I suspect the nameless guy who asked for help in class and became Ron's new lab partner when Linda was kicked out, but really it could just be any one of the freshman characters whose last names we don't know.