Hi Chris, totally aware of this 'production fun'....One acad 2000 dxf file we sent out this week was a 'curve ball' to kind of start all this...just so happened was starting to explore moi3d workflow with dxfs at same time...last few jobs been done on a cnc with better software. Exported a file from a drawing package (dxf with splines) and works fine on newer system not on the other (waterjet). Amazingly fun because these machines are not that old. Today we will start to understand/document which machine software takes what flavour of dxf, this is just so we are not guessing in future or wasting time exporting lots of versions. Luckily, we have now standardised what machine(s) our work goes on. Typically or where possible we prefer to use to just polylines + arcs. Straight polylines no arcs or splines is similar to what " r12" does and we've also used a few times. Whilst approximating arcs and curves with lines is not ideal and can up the node count (a lot) seemingly works on every system and the cam bods might then use a chain or join command, to make the machine/gcode run nice.

@Michael - having r12 dxf export option in some instances might be useful,
but I will test your polyline export 1st :0)

-- Stefano