The system is weird to say the least.
There was this period of drought i had from the Pirate update right up until the Gadget update where i got nothing except Bea.
When the update dropped i got Jacky alongside Mr. P, and throughout the rest of the months up until now, i consistently got a brawler each month until i managed to unlock all of them in the Surge season.
After that, i've only gotten Rude Sands from boxes and that's it. I'm still missing Gale's SPs and now Colette, so right now all i can do is see how this plays out.