Originally Posted by BobFL
Yep, I have....
When HEAD changes the designs on their pro sticks, it's not a small production and it takes some effort. Some of the no-mark racquets are early versions they supply their top players with before the new paint jobs arrive for distribution for all the other pros. I don't think the codes have anything to do with the string pattern. It's more the material composit and length. Any one of those could be made into a 16x19 mold or the 18x20 mold. It really depends on what a particular player prefers.
You can clearly see that Chardy uses the 18x20. If you look at any of Murray's pics you will see the same... Although it is concievable he had used both at one time or another to try. He goes through more racquets then anyone else.