I am perplexed why Build 1511 is considered up to date in my context.

On one of my backup computers, I installed Win 10 Pro during the period for free upgrading ((I still have Win 7 on my other computers).

Today, I figured I would see how far it would update (the last time I had it do updating was on August 10 last year).

It added stuff today, taking me to "Version (OS Build 10586.9.16)" and telling me that the computer is up to date.

I understand that my build, 1511, is up to date, but I am perplexed why it was not at least upgraded to the Anniversary Update, Version 1607, almost a year old. I see no evidence that advancement of the build was even tried yet. Should I try again tomorrow?

https://support.microsoft.com/en-us/help/3159635/windows-10-update-assistant

The above will help you update to the latest build.

If that`s what you want, Why aren`t you doing a clean install of the AU ?

You can do the upgrade manually. That's my preference anyway, as it's under my control.

Before you do, such an upgrade being a risk, do create a disk image of your presently working system (E.g. Macrium Reflect (free) + its boot medium + external storage for the images). A few people have major problems after a big upgrade, and that's two builds in your case.

The Tutorial section can guide you on getting an iso and the upgrade
- just search the Tutorial index for those terms.

When you upgrade, disconnect all unnecessary peripherals, and best to uninstall any AV.

As to why your PC has not been offered an upgrade- MS maintains priority lists for delivering upgrades. Perhaps your system has somehow fallen through a crack in the system?