IMM76Q was an incremental update (still ICS) that was in testing and was either supposed to go out OTA, or only meant for replacement devices/new devices sold from the end of last month onward.
For reasons unknown, it was never pushed out OTA to anyone that already had a GNEX. If you needed a warranty replacement, you would likely get a refurbed handset with it, but other than that, nada.
The updates main purpose was to gimp universal search, and there are some unverified reports of something having to do with the radio code changing (although on the surface it does not appear to change the radios). This was because of the whole Apple patent thing with the GNEX last month.
It might not have been sent out because JB deals with universal search differently, thus making the update pointless, since we know that Verizon now has a fresh JB build in internal testing.
There's really no point to this specific OTA anymore, but like the post above me states, you can manually load it if you desire.