I’ve had experience with vendors where during a manufacturing process validation they become uncooperative. In our case, we were trying to find all of the steps of manufacturing that contain water in our product components. We can only document so much internally until we get to a supplier who gives us a component. While they were willing to give some information like general process diagrams and VERY general specs, they were not willing to go specific. While frustrating, this is actually understandable. It usually isn’t a good sign when a company you supply starts asking very specific questions on how the product you supply is made: it can sometimes be a tell tale sign of an incoming audit. In addition, it is generally not a good practice to disclose all of the business secrets of how you make a product to just anyone who asks.
In order to mitigate this tightening of information flow, you can explain to the supplier why you wanted the specific information you asked for. Some suppliers will be understanding and give you what you want. Others may still refuse to cooperate and will not give anything unless they are subject to an audit. You can improve your chances with good communication, but sometimes it’s just luck of the draw.