This *may* shed some light on the issue (one has no idea how reliable the source is):
http://www.gottabemobile.com/2013/1...android-4-4-kitkat-update-roll-outs-detailed/
Also remember there was a bug in the O build and that is also why the OTA updates were stopped for all Nexus devices. If I remember correctly, it had to do with devices that had encryption enabled on their devices. So the bug was corrected and new OTA updates were created (S build), the issue effectively delayed the roll out of the OTA updates by a week or so.
On that note, I flashed the O build on my N4 and N7 when they were released and then flashed the S build on the N7 only when that was released. Still waiting for the S build via OTA on the N4.