I googled ancient Greek Virtues and came away with those four.
Each of us undoubtedly can add virtues we can aspire to. For instance, I would add Kindness, and Empathy.
I think those two observations are key. There's nothing magic about "virtue" or its classifications. But Epicurus was developing his philosophy in a cultural context in which certain words were used to refer to certain things, so he chose to work within the paradigm so as to be understandable. But the whole concept of virtue is meaningless except in reference to a goal, and the goal is not virtue itself unless you presume some god or other authority made it so. In our case the guidance of nature is to pursue pleasure and avoid pain, so whatever choices in reality and in total effect achieve that goal should be considered virtuous.