PC numbers are far too low.
The Witcher 1 sold 1,7 million copies on Steam alone http://steamspy.com/app/20900
The Witcher 2 sold 2.7 million copies on Steam alone http://steamspy.com/app/20920
Mind you, the Witcher is a GOG original franchise, meaning it sold a ton on GOG as well.
The Witcher 3 will probably sell 4 million on PC, maybe even more.