An office printer had an option for automatic duplex printing, but not manual.
I commanded it to print firstly all even pages in normal order, and they ended at the paper output tray face-down (p. 2 was at the bottom).
Then I turned them upside down, and placed them back into the paper feeder tray. Now p. 2 faced up and was the top-most sheet. See the images below.
3. I printed all odd pages in normal order. At the paper output tray, the bottom-most sheet contains p. 2 (facing down), p. 1 (facing up; reverse of p. 2). The second bottom-most sheet contains p. 4 (facing down), p. 3. So the front-to-back order is wrong.
How can I rectify this with the printer, rather than wasting my time flipping manually? I was foolish not to read this first.