I have purchased several Pioneer head units in the past year and was wondering how you faired. You get major kudos from me for your perseverance.
FWIW, I took my 7000nex out of my car over the weekend and discovered that there was no sticker on the units body indicating a SN. There is no evidence of a sticker being there either. The only places I have a SN is on the box it came in and on the yellow paper requesting that the product be registered.
After thinking about for a while, I remembered Dana from IdataLink hd sent me an email when I was trying to install an RR.
Here's a cut an paste from the email regarding SN.
"Some early production NEX radios don't have the label. If the production of your radio is before the dates listed below, you need to power up the radio and get the device number from inside the radio. When you power up the radio, go to: Settings> System Information> Firmware Information.
Model number and date
AVH-4000NEX/XNUC 05-May-14
AVIC-5000NEX/XNUC 06-May-14
AVIC-6000NEX/XNUC 07-May-14  
AVIC-7000NEX/XNUC 07-May-14
AVIC-8000NEX/XNUC 07-May-14"
Wouldn't you know it that the 1ea 4000, 1ea 7000 and the 2ea 8000 I purchased ALL have a Feb 14 manufacturer date on the box. They were all purchased in October 14 from the same dealer.