The Star Wars Wiki says, “While C-3PO underwent a memory wipe, R2-D2 was allowed to preserve his memories.” And I am delighted, because 1) I was pretty sure this was the case, but couldn’t remember exactly (R2 is a conniving sneak and I was pretty sure it wouldn’t have worked even if anyone had been foolish enough to try), and 2) this means one of my favorite Star Wars headcanons is actually canon.
It means that during that one scene in Empire Strikes Back, these two assholes know EXACTLY who the other one is.
You are decorated war veterans, you absolute trolls.