GC was approved today. Looks like my theory was partially right. I suspect fingerprints cleared on 9/23, and the GC was approved a week later. It was a shorter time at CSC than those who didn't have an RFE.
Best of luck to everyone waiting on their process to complete. I'll keep posting updates as card is received, etc.
-ML
K1 -> I-485 -> I-751 -> N-400
Now filing I-130/I-485 for parent...
DO: Santa Ana, CA
5/13/08 - Parent I-130/I-485/I-765/I-131 mailed to Chicago Lockbox
5/22/08 - checks cashed, receipt numbers from Missouri MSC (NBC)
5/25/08 - Notice dates for all notices
5/29/08 - LUD I-130/I-485/I-765/I-131 (received and pending at NBC)
6/07/08 - Fingerprint appointment letter received
6/12/08 - Fingerprint appointment date
6/12/08 - LUD I-485/I-765 (no change, still received and pending at NBC)
7/29/08 - LUD I-485 - RFE sent out, case on hold
7/30/08 - LUD I-485 (no change, still on hold for RFE)
8/04/08 - RFE received, request for tax return, 87 days to respond
8/05/08 - Sent RFE response to NBC (regular mail)
8/14/08 - LUD I-485 (RFE received, case processing has resumed)
8/15/08 - LUD I-485 (no change, still case processing resumed)
8/18/08 - LUD I-485 (no change, still case processing resumed)
8/18/08 - LUD I-765 - EAD approved / card production ordered
8/18/08 - LUD I-131 - AP approved / approval notice sent
8/19/08 - LUD I-131 (no change, still approval notice sent)
8/26/08 - AP received, multi entry valid for 1 year from 8/18/08
8/29/08 - EAD received
8/30/08 - Case transfer to CSC (letter received, no web update)
9/03/08 - LUD I-485/I-130 (case pending at CSC)
9/04/08 - LUD I-485/I-130 (no change, still case pending at CSC)
9/23/08 - LUD I-485 (no change, still case pending at CSC)
9/29/08 - LUD I-130 (no change, still case pending at CSC)
9/30/08 - LUD I-485 - Card production ordered
9/30/08 - LUD I-130 - Approval notice sent on 9/29