Updated Database of SPs (2021-05)

According to the previous post in the category, Updated Database of SPs (2015-06), it's been nearly six years since I last updated my database that cross references posts to start positions (SPs; see posts from the years 2000-2002). Even after such a long time, I had slightly more than 20 references to add. That's mainly a comment on how little analysis there is on this blog.

I suppose I can do better than that, but there are so many other chess960 angles to explore. At two posts a month, how much ground can I reasonably cover?