I remember years ago reading an article somewhere which talked about the pyro guys trying to perfect the Mickey when they first began doing him in the fireworks back in 2000 in Believe..There's Magic in the Stars. They said they went out to some place in the middle of the desert and would try different types of shells to see which worked best until they finally have what there is now. So they do do some testing in the desert somewhere. Then they will come do more testing at the Park, which is what they did for Remember.
Who knows, they may be working on some new-type of shells right now in the desert for the new show for the 55th Anniversary next year. Never too early!