In the PC-DMIS I worked with briefly, the positioning was always from the Machine Coordinate System (MCS). You can rotate the measurements and translate their positions based on datums, as you did. However, only the 'real' curve that was measured will be in the program.

I suspect you will have to measure both curves separately. I am not a DMIS expert, perhaps there is a way to create actual points without physically 'scanning' the points "on the other side" at least once, but I doubt it. Your process of evaluating both curves based on a single nominal will probably work once the other side is in the program.

You did a better job of communicating the problem in English than I would giving you an answer in Italian.

Ciao, and good luck.