Just discovered the hard way you need to backup the vendor file in TWRP when doing backups. It''s not selected by default. There are 2 options "Vendor" and "Vendor Image" - I believe "Vendor" is the correct choice, since TWRP doesn't support flashing the vendor.img from within TWRP. Hopefully it will restore the "Vendor" option. I tried to restore my Stock Rooted Image and the phone boots, get's the popup about the phone being corrupt and then can't be pin unlocked. That's because I was on 08K stock and flashed the 08M Vendor.img to match the ROM (Part of the install instructions) Not sure if that's because I changed to a different pin when I flashed PureNexus and the Pin is stored in the vendor image or what. Tried both Pins to no avail. But I think I can re-flash the Vendor image for "K" - not sure if I'll be able to get it to unlock though. Not a disaster by any means, had a backup of the ROM so I'm back in business and of course we are the truly lucky ones who can get stock image file to flash in Fastboot. So just a word to the wise.