Over the past few weeks I have been pretty busy with work, so I've just been somewhat mindlessly logging into my nation to keep tech deals going, collect when I need to, etc.
Today I logged in and realized my NS was a bit lower than I remembered it being. Looking at the chart for nation strength history, from 4/5 to 4/6, my nation dropped 29,500 NS. The interesting thing is that I am not sure why. Nothing has really changed, no events or wonders expiring, no buy/sell of anything (including military) beyond receiving tech, or anything else I can think of that would adjust NS like that. Unfortunately I wasn't keeping close track of my tech or land amounts so I am not sure if either of those changed (they shouldn't have as I didn't sell anything). Fairly certain infra levels did not change. Was there a game mechanic change in NS determination?