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There are two conflicting ideas here. The ruling on mass band has always been that they enter battle at the same time, but their SA's activate sequentially. However, the definition of having entered battle says that a character has not entered battle until his SA has activated. One of these rulings needs to be changed, and I vote for the change being made to mass banding.
Not that I know of, but there had to have been a reason for "characters have not entered battle until their SA's complete." Doing away with it because we don't remember the reason may have unintended consequences.Either way I'm still a proponent of mass banders entering one at a time. That's easier to explain and simpler.