Here's an update dear readers! I foolishly assumed that "completing research" meant both loading it with KP AND activating it. So as the FA had started, I decided not to activate the research - thinking that I'd still be officially in Chapter 18 until I did so.
But ... it turns out that just loading the "Prepared Barracks" research with KP (start of Chapter 19) WITHOUT activating it, still counts as completing that research and starting the chapter...
Thus when I added the KP, I unwittingly started the new chapter, and increased my burden for gaining the level-related badges (coins, bracelets).
I found this out tonight when I activated the research point and didn't appear to receive the 200 diamond reward. When I messaged Support, they said I'd received them a few days ago (when I loaded the research spot with KP). I didn't notice at the time as I was busy with the FA.
We live and learn eh!