Adding files to existing (and ongoing projects)

Good  morning!

I wonder if anyone has had the same issue: I have a client for whom I translate a magazine twice a year. The "problem" is that they do not send me all the files at once, but usually in the course of 4-6 weeks. This means that I start the project with very few files and then have to find a way around adding the other files to the same project. I have "forced" this up to now by manually adding the new incoming files, closing trados and reopening it. But I am quite sure that this is not the right way to approach this. How do you approach this?

Thank you!