If the topsheet and sponge has to be certified together this means that all players using modified sponge hardnesses then have to what, get ittf approval for a whole new rubber? What if a player is using a 52.5 degree sponge instead of a commercial 50 degree for example. Are the limitations on all of the exact specs or just on the composition material and formula for the sponge?
When buying rubber at retail, there is variance. A rubber marked 50 is not 50.00000, it is 50 plus/minus a degree or so. What is the tolerance for sponge hardness in the Joola contract with ESN for normal retail product?
Any product for pros can be simply chalked up to normal manufacturing variance. Rubber makers can claim that they make many batches of rubber and simply do a quality sort where they measure individual sponges for sponsored players. Sponge batch X was supposed to be 50 +/- 1, but it came out and tested at 52.5.