I may actually be getting the hang of this after ten years (yes, this thread is 10 years old!!).
I only bought 68 books last year (2020), I've bought 40 so far this year, which means I expect to buy about the same this year in total.
That compares to 166 in 2019, 194 in 2018, etc, etc.
I'm not sure what's worked. I think a combination of all the rules we've come up with over the years.
I hope that others manage to meet their buying goals in less than 10 years.