When an I-485 is accepted at the Service Center, requests for FD-258 FBI fingerprint checks, fingerprint fees, and G-325A consular background checks are made by USCIS. Responses to these requests come back to USCIS and must be matched up with the appropriate files held in staging. File Maintenance "file connects" these responses to the corresponding files.
My wife and I had our passports stamped after a 6 hour ordeal that started at 8:30 a.m. and ended at 2:30 p.m. Here are some tips based on what we experienced,
1. For an 8:40 appointment, get there before 8 if at all possible. They were not checking appointment timings, so people with 9/10 a.m. appointments were ahead of us in the line. All they care is that you have an appointment for that day.
I had an interesting N-400 interview yesterday. Don't know where to start but the IO stemmed out of the office with my thick file while I was waiting for my attorney to arrive. I quickly summed him up to be a hard ass. BTW, I have been an officer of the law for a little over four years now...My attorney arrived shortly after and we went to this small conference room. I was sworn to tell the truth, and the interview started.