It's so close now to being finished. I had a couple of very good writing days recently and Book 18 is presently about 41,500 words and should be finished around 45K words.
I've had to resolve some small plot holes, but that's always part of the writing process. As things get sorted out, the story gets better and better. I didn't have this planned out the way I should have, but it's turning out better than I could have planned anyway. It's just not what I would have expected. You'd think I'd expect THAT in this series by now, but the individual books still surprise me.
When it comes to writing, you have to be willing to let go of what you expect and let the story become what it needs to be. Once I let go of what I had wanted, the story sorted itself out.
I hope to finish this soon. I'd like to get done and then edit Book 16. I want to publish GHOSTS before the end of February, but it's going to be tight.