I notices that when milling a board who’s NC code was generated by Copper CAM, there is an offset between the drilled holes and the etching of the tracks.
Once I drill the holes, I’ll enter an offset of X-1 and then zero Mach3. That shifts the subsequent steps (etching, cutout) by 1mm to the left.
On closer examination, 1mm may be too much. I will try 0.8mm on the next board to see how it turns out.

UPDATE:

It turns out that my mill is not perfectly perpendicular to the board. The error comes out of the fact that the end of the tool for the engraver mill and the drill is much different and when a small rotation is added to the mill head a linear difference is observed.
I adjusted the head rotation and now both the milled and drill points line up perfectly.