> They'd say, "Send us X," and I would reply, "What do you mean exactly by X?" and they'd reply with, "Send us Y". A black box.

Thank you so much for talking about this. I will never work for, nor be a customer of, a company that operates this way. Their culture is obviously one where the leadership have not impressed a need to have clear and continuous communication around business-critical processes. There'll be many more problems related to this.