The Agile Manifesto never came out and said so, but it only ever made any sense if you give up the idea of a fixed delivery date. Of course, the idea of a fixed delivery date for a software project never made sense in the first place, but you’ll have to pry that nonsense from their cold dead hands. Big-A “Agile” is an attempt to keep what they (think they) want… so it ends up being useless.