I’m pretty confident they didn’t buy an American product… 
My machine is sold as a 20x12", the actual working area dimensions were 500x300mm (5030 type), this comes out 19.68x11.81".
I put a different head on mine, so I have a choice of which axes I can extend. I picked 504x340mm. The table screws are in the way to use all of the area.
Left is the X axes limit, right is the Y.
Keep in touch…
Surprisingly, the belt around the platform leadscrews in my machine has a perfect 0.2 inch tooth pitch, which I absolutely did not believe until I counted exactly 50 teeth in 10 inches. Every tenth tooth lined up neatly with successive inch marks on the scale.
If it was the more believable 5 mm pitch, then Tooth Fifty would be at 9.84 inch, but it definitely wasn’t that far off.
The world is chock full of mysteries these days … 
