The update has yet to be pushed OTA (over the air)
Shortly after Google started the rollout of the Android 4.2.1 update to Nexus 4, 7 and 10, the update has been made available for manual download to all Nexus Takju handsets.XDA Forum Junior Member dmapr managed to get his hands on the small update and it’s now up for grabs via AndroidPolice.
Keep in mind that, for the time being, the update can only be flashed on Takju Nexus smartphones, meaning those Nexus units purchased via Google Play store.
The Android 4.2.1 is a small 1MB update that packs some bug fixes, including the December bug that was discovered not long ago after Google released Android 4.2 Jelly Bean.
Before trying to flash this small software update, you should make sure your Nexus Takju runs the Android 4.2 JOP40C version. No word yet on when the update will be pushed OTA (over the air).