one of my friend is in same situation...his case was already approved as LPR,when he became citizen he email his certificate(naturalization) to nvc...
about checking case status at nvc,i think you should call them...
I-130 for parents
09 June,2012-Applied I-130 for Parents
15 June,2012- Check's Cashed
19 June,2012- Case number received
08 September,2012- Received approval notice
RFE ,docs sent on 31st dec 2012
01 Feb 2013-Interview letter received
I-751 for wife
25 September - I-751 - Sent
27 September - I-751 - Delivered
02 October - Check cashed
04 October - Extension notice received
13 October - Received bio-metric notification (Fingerprint notice - Scheduled for 07th Nov)