Yep, no microphone hole on the late 2012 27” iMac. I followed the video but I don’t think it made anything easier.

Maybe my mistake was putting the screen back on when the frame was lying down. I was left with a mm gap on one side due to misalignment. Stand up the mac so the screen can sit on the lip and be aligned properly.

For the late 2012 27” iMac, strip 23 didn't line up correctly with the antenna. the antenna adhesive was a cm off from where it should have been. No biggie though.