While we can never know the exact population of any large scale entity (even a city is unknown, let alone the whole world) we can make a reasonable approximation, and a year here or there does not make any difference to the global scale impacts over the coming decades and (hopefully!!) centuries of the human species.
The UN will mark 15 November as the day on which humanity reached 8 billion people. This will draw attention to the patterns we see in fertility and population growth and how they impact on the quality of life and standards of living of people around the globe. In my school days we thought the world population might reach 20 billion!! Now it has reached 8 billion 12 years after hitting 7 billion and is expected to take 15 years to get to 9 billion and stabilize at 9.7 or so. This is good news as with a slowing rate of growth and a ceiling not too much more, planning for resource distribution and sustainability can become much more accurate.
Genius is one percent inspiration and ninety-nine percent perspiration.