OK, it’s taken me a few months to get around to finishing the story, but it turns out that it definitely wasn’t fewer changes that helped us get through the backlog quicker last September. Looking at the number of changes for the whole month of September, we can see that there were actually more this latest time around.

Chart showing monthly updates to Grouper groups, by stem, from August 2016 to September 2018

This leads me to conclude that my theory about PSP having less to do is most likely correct.