Thanks, I did not know that, mainly because the program I used to generate the DXFs (Adobe Illustrator) did not offer any option for version choice.

The larger thing I was solving is to get a proper workflow from 2D vectors derived from old maps, done in an Illustrator file, into a format that joins it with 3D shapes derived from it, and then be able to export it into a format Unity can take in order to build an application around it. All on Mac. For the moment I found I can export to Illustrator 8 (a really old version) and open that in Maya, from where it can be exported as FBX.

The much better way I think (and I am pretty surprised it seems to be this much of a 'niche' in terms of solutions, for a project that perfectly falls within the professional boundaries of digital heritage applications) would be to get everything (2D, 3D) in AutoCad and be able to export straight from there. But not for Mac users, apparently...