No, as far as I know, it's not written in the materials. And Dov is right - ultimately, the true reward, and the most valuable reward and celebration, is the fact that I've been clean for another glorious day - heck, another glorious second!
But sometimes, it helps when we make a little party, to remind ourselves, to shake ourselves up and to give us the perspective that "yeah, this IS something that's worth partying over."
True, it's worth more than a party. But at least it points me in the right direction.
The key is to remember that being clean is a privilege, it's something to enjoy. It's not a burden, it's a gift!