If you wait for the alpha and beta testing, which should be actions that verify the system developed meets the requirements, it seems to be too late. User feedback should be done prior to any development and should be done by the project sponsor as verification that they know what they are talking about when explaining the requirements of the system to satisfy their business need. Some will base requirements on what they create, while others create based on the requirements defined. Which system would you prefer to get delivered for your business?