Renault had to build 2500 Ragnotti/Cup versions in order to get a number of changes homologated into the FIA book. To homologate a car requires lots of paperwork describing the technical bits in great detail, and proof that the number required was built.
With the Ragnotti, Renault got a lower minimum weight, wider track, lower ride height and probably a couple other details which make a difference on the circuits and stages. You would have to read the full homologation papers to tell exactly what they did. Even such things as gear ratios have to be homologated.
There are many famous photographs of a yard at the Porsche factory with all the cars of a certain type assembled together. They did it for the 917 and the SCRS, all 20 of them, as they were a Group B evolution. In group B, only 200 cars needed to be built, and 20 of an Evolution. In Group A and N 5000 used to be required along with 500 for each evolution. The present requirement seems to be 2500.