I thought I'd been reasonably clear with the description of how these frames are built, the final accuracy is achieved by boring, not reaming. There are several really interesting videos on YouTube that show the vast scale of this kind of production, and at scale CNC machining and complex jig investment becomes economic.
For example, Fuji-Ta/Battle produce over 12 million frames annually;
The manufacturer is producing a replacement frame, and air freighting it to me; I expect to receive it in the next couple of weeks. I'm not confident it will be better, but hopeful that it will be. I'll update when I know more.