if the aim is to "to assess whether a product is unchanged before and after implementing a change e.g. in a process", then

recouvrement = overlap i.e. "pourcentage de recouvrement" would be the extent of the "overlap = similarity" between a product before and after implementing a change in a process.

pourcentage de recouvrement = 100% would mean the product is exactly the same before and after a change in the process.

pourcentage de recouvrement = 0% would mean the product before and the product after changing the process have absolutely nothing in common, that after changing the process, the resulting product has been changed beyond recognition.

Doesn't matter at all what is "the product" or "the process" used to make the product. The method used is clear enough: make some changes to "the process" and mesure "le pourcentage de recouvrement" i.e. to which extent the resulting product "overlaps" with the product obtained by the same process before the change.

ALL THIS ASSUMING THAT "recouvrement" IS NOT PART OF THIS "process" which is yet to be confirmed so CL1.