Yes. There are a couple of ways to do this. Both don't cost you any credits. It's free as part of your plan.
Every book has a merge button here:
When you click on the book you'll see this..
Just click add more books. Then repeat the process with all the books you want to merge.
Then click "Build Merged Book Now"
2. Or you could use your "search archive" view to get to this. Click "search" in the top right menu.
Then you can browse all your coverage by client, date and search term. Then export to CSV (to get totals etc) or even create a new book from the results. (for free).