Unless we are talking the possibility of two 55th North Carolina Infantry Regiments...I believe it was organized in May 1862. It then served in the Department of North Carolina until it was assigned to Davis's brigade. This regiment, although it had some very minor engagements prior to Gettysburg (including a minor skirmish at Suffolk), Gettysburg was its first real battle. I do not believe this regiment was with the ANV at Fredericksburg, nor were any of the other regiments that would comprise Davis's brigade.
Correct. The 2nd and 11th Mississippi were old timers in the Army of Northern Virginia but the 42nd Mississippi and 55th North Carolina were still fairly untested. Gettysburg was their first real test.