I just learned the same lesson my last project. I got most material only after the original deadline and furthermore no-one had even really looked at the stuff

I just learned the same lesson my last project. I got most material only after the original deadline and furthermore no-one had even really looked at the stuff I had coded before that (using placeholder media). Which forced me then to take a lot of unpaid "free" days in my follow-up project just to handle that stuff as it arrived. And certainly still having an old project in mind while coding at something else already was just plain horrible. So yeah - I will also make sure next contract mentions that the client has to deliver it's part or that there is at least some compensation otherwise. I had even thought about that when doing that contract, but got persuaded otherwise as the company seemed to want that deadline so badly for themselves that I just didn't expect them then to just push it internally for a month.