[member="Nightmare"] Traditionally, a cell system is affected so nobody knows each other's names, even by code - let's face it, if you refer to yourself by a code name, and someone else knows that code name, chances are it can be zeroed in on you. Even an adversarial intelligence-gathering agency would put patterns together on that one, potentially track your movements or figure out what you're up to.
Let's be honest: if you wanted a code name system, you'd randomise and change them after every assignment. You'd end up with a few dozen code names, but even if someone was compromised, it'd be an irrelevance, since that identity would cease to exist thereafter.
Or you could just stop referring to each other by names altogether
[member="Coci Heavenshield"] I know what the Shadows are! It's the code names I found odd. Surely you'd just be normal Jedi during the day, but have secret assignments that would occasionally take you elsewhere. No code names necessary!