It has been at least 2 or 3 (if not more) seasons where I have achieved a reward status for a quoted number of cards (this time 12) but received at least 3 fewer cards in my rewards than the quoted number of rewards cards.
Is this a glitch or are you doing it on purpose because you can? I would hope it's a software issue.. but considering it has occurred for so many seasons, I'm slightly confused...
EDIT: thank you to 
What is being done to review and resolve this issue?