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.
We won both an EB1 Alien of Extraordinary Ability case and a National Interest Waiver for this applicant. He was noted as being an exceptionally qualified, brilliant and outstanding researcher amongst an international peer group. We provided copies of his substantial publication record as well as evidence of his numerous "invited" presentations. This applicant had patented material which was identified as innovative and pioneering in the field and admired by top researchers.