sure you are right ! it's 21 days on my current entry stamp ! I explained it wrongly, sorry !
I had a stamp the last time I went out and through my METV (which already ended on the 13th of June). Then I did a one-month extension and that is my actual stamp. It end on the 10th September !
Immigration also told me when I will be back I will be able to apply for the non migrant b and the work permit. And it would not be necessary for me to go out again to get the non migrant b and the work permit ! I was a bit surprise about I dont have to go out again... because most of my friends who work for others compagnies, they had to go out to get it. Do you know something about that ?