My evidence :
۰In Vs The Tango when Chuck says his alias will be Charles Carmicheal she responds b saying that that's a good cover name, nice and close to the truth.
۰When she and General Beckman are conferencing in private, she still responds to her as Sarah, or Agent Walker.
۰At the end of Vs The Lethal Weapon, we see the back of Chuck's Tron poster, on it he is questing for her real name.
It has Sarah Walker on there, then crossed out, but it is re-written on there, see ? :

Wow, posting that, I noticed something else. All other things, incuding the crossed out version of Sarah Walker had ?s after them. Where Sarah Walker is rewritten, you see NO question mark !
:O
So what do you think ?
Appreciate your theories !