Remind me again how key fragments are handed out?

Just for clarity reasons only, I thought that key fragments were given if your team wins, with a higher drop rate per additional member of your premade. Well, even though I am soloing, they still drop. So how come in the last 9 wins (6 of which I scored an S- or better, but I believe that is for the crates) haven't I earned a key fragment? I guess it could be just bad RNG luck, but... I have not experienced this many wins without getting one before. My only thought is that you only can get one fragment per day, since these 9 wins are all from today, but I dont remember reading anything about that.