Just received the October 05, 2016 Security Patch - 46.3meg on my Nexus 6p. I usually receive the OTA patch mid month, but it came early this month.
I also received mine today. Odd that the security patch is postdated. Just like you, I usually receive it mid month.
I don't find the date strange. By the time I received the OTA update in NYC on 10/04/2015 @ 17:15, it was October 05, 2016 on the other side of the world. What I do find strange it that I received the update so early in the month. I hope this trend continues for all future updates. No problems with my N6P after the update.
Are you in the beta program? The build number is definitely beta, and that would explain the predating if this is to test to make sure the official monthly update doesn't have major issues before being posted.
Are you in the beta program? The build number is definitely beta, and that would explain the predating if this is to test to make sure the official monthly update doesn't have major issues before being posted.
No. It's not beta. It's official release.