Maybe 500 words; a little more excavation.
Also, I did more work defining the aim and the intentions for the structure. I'm currently aiming at about a 60,000-word draft, and I have currently about 17,000. In other words, I've got a lot of writing to do to get to the complete draft that I'm imagining. All the more reason to focus my efforts more intently on trying to write, and on committing to getting writing done regularly.