Every month, on the exact same day and time, Donald got an envelope with cash dropped on his doorstep. The person claimed to be an old friend, but Donald knew it was Scrooge, but he didn't want to talk to him, so he let him, and just never spent the money. (Except when he really needed to) Years later, when the triplets are 9, he finds out who really delivered the money, and it's not who he expected