Trying to avoid spoilers here...
There are two objectives in December, let's call them A (involves doing something in several cities) and B (the other one).
When I complete B, the game asks me to do something irreversible.
If I complete B in December game 1 and then lose that game, must I complete both A and B in December game 2 in order to win it? Or is B considered to be already completed since I did the irreversible thing?
When you complete B, you then do a thing.
Spoiler (click to reveal)
Scratch off the card
It actually explains what to do in this situation.