I completely missed a good millstone of my own, but like I always say, I never think to watch those things.
I usually only know because someone else mentioned it or captured it.
With alerting people that their millstone is coming up, preserving the millstone, offering congratulations to the person for each millstone, and then the person who has the millstone saying thank you for the congratulations -
That's got to be effective for adding posts and even pages.
And adding pages makes for a happier BK!