The author's last update in April says he's finished the Antietam chapters, and is moving on to Shepherdstown etc.:
I have finished the last two full chapters on the Battle of Antietam, covering the 9th Corps assault on the afternoon of September 17 and A. P. Hill's counterattack. Other than a part of the next chapter to cover the disastrous attack of the 7th Maine at the Piper farm this concludes my 18 chapters on the battle. Now, it will be on to the end of the campaign, aftermath, etc., to wrap up the manuscript. This is no small task but I see the end to this massive project now.
As I was working on these chapters I thought possibly some people might be interested in how I assemble my notes for a chapter. The process has changed over the life of this project. In my first chapters I had files and books spread all over my study and numerous files open on my computer. I would not call this a system. Chaotic and time wasting are better descriptors. Maybe it works for some people but I found it maddening paging through books or searching through files for that great quote you were sure you could find easily but a half hour later still eluded discovery. Or, there were the times you lost your grip on a fat file and its contents spilled out all over the floor. I decided to create an electronic notes file for each chapter. To do this I read through every source I have relevant to the chapter I was working on and typed into a single document anything important or quotable from that source. This is time consuming but it has two advantages. First, the process of both reading and typing sources familiarizes you with the source material and often reveals patterns that would not otherwise be noticeable. Second, when you finish you have a single document with nearly all the source material you need to write that particular chapter. As an example, my notes file for Chapters 17 and 18 is 83 pages long and 57,000 words. It could have been longer but I tired out trying to enter all the little details from the many different artillery batteries involved and just used the old-fashioned search, find and read process I had followed earlier for some of them. Battle chapters notes are organized by order of battle so it is easy to find what I need and a Word document is searchable, so tracking down a specific quote is simple. With everything in one place I have found writing flows more easily and makes it less likely that you may miss something important. Everyone who writes history has their own way of taking notes and using sources. I don't advocate that mine is better than anyone else's. It just works for me. I hope you all stay safe out there and that you are finding some time during this pandemic to get some reading done you've been wanting to do. I just finished Will Greene's A Campaign of Giants, about the first couple months of the Petersburg Campaign. An outstanding work.