According to Gilchrist (in his autobiography) they are all one type of bat (can't remember as it's been awhile since I've read it and cbf'd searching for it right now) and then they whack the sponsors stickers on.
Gilchrist used a Millichamp & Hall Puma his whole career. Julian Millichamp has a signed bat in his workshop from Gilchrist saying something along the lines of "greatest bats in the world."





