Yep. That’s typical software development too. The business requirements are never very well defined. They promise smoke & mirrors and that’s what they get.
Yeah, I’m in a critical project now where we will develop requirements somewhere around go-live. It’s too important to do it right this time.
Of course, that makes my job easier. I write requirements. Just take screen shots of the deployed software and describe its behavior. I’m as much in the dark as the developers this time.