The data set doesn’t measure EVERY game sold, but instead every game that sold at least 10,000 copies. So if a video game system had a large number of low selling copies, it might be underrepresented. Because of the market for consoles right now, this is most likely a larger problem for older consoles and handhelds than any of the modern ones. The data set also only goes partially into 2017, which is obviously not the full life cycle for the current generation. So comparing PS3’s entire life-cycle to PS4’s partial cycle might not be entirely fair.