If you have an A # in the passport then it should be fine. I was the opposite. We had the I-181 with the A #. However the stamp in the passport did not have it. When I went to USCIS and told them the situation they updated the passport and put the number in there. Not that it really mattered in the end. I was unable to get my son a SSN until I had the green card as they did not recognise the I-181. Bureaucracy!!! If you have a SSN then I would say your in the system some place, so just take what you have to the interview and you should be fine. The place I went to in Houston was wonderful. It was not busy and nothing like the SSA. I was there for an hour or so though, but that was at the counter talking to the agent. Just make sure you take some passport photos too, as this seemeed to be the biggest issue they were worried about. "How will we get a photo on his green card they kept saying" I kept telling them, "Here I have 8 photos, take them all, its the same photo of his passport so you can use that"