If you get the yellow key and save beauty bomber instead of the blue bomber girl you will unlock a special mode that allows you to unlock the rest of the cards for the treasure chest (to get the treasure chest beat star bomber's high score in attraction mode) you will notice that there will be 7 cards missing. You get the last 7 cards by beating the special mode up to stage 25. Then it will tell you, that you have unlocked the special title screen.