Nikolaj Schlej has written the first of a series of articles on NVRAM file formats:
“NVRAM formats of UEFI-compatible firmwares”
It is in Russian. If you don’t read Russian, there are many C structs and colored screenshots that are self-explanatory, and auto-translators (like Google Translate) work pretty well.
If you’ve not been watching UEFITool NE recently, there have been lots of checkins for NVRAM formats.
https://habrahabr.ru/post/281242/
Nikolaj is also looking for some NVRAM formats for testing:
Firmware Security 