What can happen to the project if you didn't have enough related data and information?

unfortunately this is a common situation for most of the projects ,as a project manager you need to fill in the gaps and try to maximize your team usage to get all information that are needed ,and fill in the information you cannot get from customer based on your experience along with your team ,the less information you have the more reserve you will plan to accommodate such rick 

The situation will be very much like a plane with no navifational/guidance systems even through the engines seem to be running normally as expected !!