I am sure this has been speculated before but most likely explanation for a wide range of notice dates that are being approved/RFE randomly is because a related application for EAD or AP triggers I-485 approval or RFE. Even at other service centers most approvals/RFE are being issued right after approval of EAD/AP application. Unfortunatley FP-2 is a poor predictor of whether or not your case is to be adjudicated soon at least at NSC.