Or to make “concatenate” more physical, divide an area into 12, one for each month in order, then in each area, people sort themselves.
This is similar to the best design we have for the fastest way to board a plane: take people in a dozen or so “chunks”, then have each chunk stand in a sorting area atop a diagram of the airplane, one chunk at a time. A group enters the area and sorts themselves by standing near the place on the diagram where their seat is, then boards the plane in line. As each chunk boards, they’re already in the right order so that nobody is blocking anyone while trying to stuff their overhead luggage.
I’m not sure if any company has implemented the system but there was some test a company did of a bunch of boarding techniques and it was the most efficient.
