4.04 is not a Google rlease, its a Verizon release. Google only released iCS Vs 4.01 and 4.02
You are mixed up about how these releases work, let me clarify it for you.
The android version (which in this case is 4.0.4) and build number (IMM76K for verizon) distinguish two different things
The Android Version number (4.0.4) is the version of android you are on. Google/Android are responsible for these releases. Google/Android release the source for these builds. Verizon has no part, whatsoever, with the version of android that google/android create and release the source for.
Now, the Build number (IMM76I or IMM76K etc..) is what distinguishes the different builds of the base source of the version of android (4.0.4) you are running. These differentiate between the phones that the base android version (4.0.4) is running on because android needs to be modified to run on the various different phones/carriers out there. When there is a bug fix release or a hot fix for things pertaining to one specific device (I.E. the apple patent infringement lawsuit), normally the only thing that changes in the update is this build number (as seen as the possible IMM76Q release:
http://forums.androidcentral.com/verizon-galaxy-nexus/186960-imm76q-software-update-imminent.html).
When the android version number increases by 4.0.x (ie. 4.0.3 to 4.0.4) this is a general android update. This update addresses bugs and adds modifications to ANY device that was running 4.0.3. The reason that not all phones are updated to a new version at the same time is because each and every different phone needs to be tested before the update is released, because they are all on different builds of android. This is where fragmentation occurs.
***----If you are thinking TLDR by just looking at the size of this post, THIS is the part you will want to read ---- ****
Notice that no where in here did i say Verizon creates any updates. This is because they do not. the Version number, 4.0.4, is modified by Google/android. They are the ones that release these different android versions. The Build numbers, IMM76K, are released by the devices manufacturer, which in the nexus' case just also happens to be google as samsung had no involvement in the software side of development for the nexus. This is also why the Nexus line is praised as being the fastest updated phones. When the manufacturer has completed and compiled a new build for its phone, it sends it off to verizon for Quality testing, at which time verizon approves or rejects the update. Verizon does NOT build their own updates.