It was many, many months ago that the owner divulged that they were approaching 5 million copies sold (including dlc) - the lions share being the base game. I took the liberty of conjecturing that during the months since that post that they might very well be closer to 6 mil by now. On that point I will allow that you “might” be right but personaly I’m leaning that they might be closer to 6 now.
Perhaps @medierra might be kind enough to pop in and illuminate - it has been a bit since we’ve had an update on that 
^posted over a year ago - May 2020