Thanks Saylin, I did call the NVC to confirm about the case complete. She confirmed it is complete ( yay!) and that the barcoded cover letter is standard when they send out checklists. She said to disregard it and to NOT send any more materials to the NVC but to bring them to the interview. I think the reason we were told to bring more supporting evidence to the interview for the US domicile requirement was that we had initially sent only the minimum required - the deed to our house and my voter registration card showing our intended address. Believe me, we will be supplying as much evidence as possible for the interview !
Thanks again for your help.