I have no firsthand experience, but a friend did this successfully a couple of years ago.
His residency was approved, but then, nothing. Nothing for a long time. Because the PM had to sign that and because at that time the political situation changed the PM at that time didn't think that is really important. That's why, after approval, my friend had to wait years to get the official documents.
So whatever you find out, remember that someone has to sign it and you can't exactly force that person to do that...