We are very deliberate about setting deliverable dates in time after the required inputs by others are available, and when inevitably they are not, we have a spreadsheet sent to the customer every 2 weeks which shows what information we are missing and the delay that is causing to our progress. As we are liable for damages if we delay the project it is necessary for us to have the proof that we did not cause the project to be behind schedule. This often means having these difficult conversations only a month in to a year long project when vendor drawings we were promised are not delivered.