Update: completing level 16 marked level 11 as complete, but not level 16
Many thanks again for letting me know, I have added and update to fix that screen for the future. :)
To calculate the Y coordinate of the level select screen to turn the box green I was using:
Round_down(level_number / 6)
That only works for the numbers 1-10. The correct equation is:
Round_up(level_number/5)
Many thanks again, really appreciate the feedback!