Where are the key fragments?

So I went on a massive losing streak a bit ago and just started to pull out of it recently. It wasn't until now I realized I haven't gotten a single Key Fragment yet which, granted, is only 8 total wins.

I thought the drop chances were reset on a monthly basis? You'd think that after 8 wins I'd have gotten at least 1 key fragment ya'know? Hell, I've gotten 2 boxes before any key fragments. Tis a sad life

Anyways, am I mistaken about the drop chance resetting or have I just had rotten luck this week so far?