Well, the AA codes signifies the following, for box 12 of your W-2. If you know that is true simply select AA, there will not be a 23 to add in your W-2.
Code AA—Designated Roth contributions under a section 401(k) plan. Use this code to report designated Roth contributions under a section 401(k) plan. Do not use this code to report elective deferrals under code D.