Oh, my fault. You're totally right.

I finally got this to work in my sandbox, and it looks like it is working mostly correctly, but it seems there is a serious delay in the calculation.

For example, I created a license as you did, "By number of users" with 2 installs per user. By manual count, I should have had 24 used, but instead the software counter reported 25.

Then, I increased the installs per user to 3, and the number of installs went to 16. Upon changing the number of installs back to 2, It still hasn't recalculated (>5 minutes later, even after clicking "count").