I'm pretty sure that model has it's own forked version of 10.12 so the dmg would need to be captured directly from it.

Even if that is not the case, I can't create working 10.12.4 or 10.12.6 NetInstall due to getting signing errors on install which is a known issue with Apple.

Even if that is not the case, I can't create working 10.12.4 or 10.12.5 NetInstall due to getting signing errors on install which is a known issue with Apple.

We are as well - although we haven't tried with the new iMacs yet - we are having a lot of difficulty imaging with a Netboot image running macOS 10.12.5.

Rather than block copying our OS DMG file, it unmounts the drive, says its block copying and then a few seconds later says it's finishing block copying.

You have a forked macOS issue. Best option is to wait until 10.12.6 is released and build off it. These are 2 sites that are good to have bookmarked: https://support.apple.com/en-us/HT201260 and https://support.apple.com/en-us/HT204319. They should you the OS and build that is shipped with each model and what builds the App store releases.

Read here

literally just finished building the forked image and NBI as above yesterday (thanks to everyone on forums!:) now today 10.12.6 dropped.. any verification that this gets rid of the need to create forked boot NBI and image?

double post

@techmchs I'm building a base OS with the 10.12.6 installer now to test with Netboot. I'll report once it's done and I've tried imaging.

While this may work for folks, I'm still experiencing the issue I mentioned in my previous post where the OS DMG file is not block copied.