Where did it all the oil go?
It stuck to the gears.You can rest easy. As long as you do the oil change every 5000km/3000m or once a year, whichever comes sooner, or some reasonable approximation of these periods, and don't ride the Rohloff through water over the hub, it is lubricated.
I had a period of puddles under the gearbox. Eventually I traced it simply to when the heating in the room where the bike stands was switched on and off by the timer. It hasn't happened for a long time, perhaps because I stopped putting in the full 25ml of four seasons oil and instead measured a more reasonable 15ml.
A certain amount of oil is breathed out by the hub. The oil in the hub is, at least theoretically, open to the atmosphere through a breather hole in the centre of the axle. If you do the math of what you put into the hub as cleaning oil and four-seasons oil, and what you recover of the cleaning and dirty four seasons oil from the previous service, by the time you do the second service there's always some oil "missing". (It also happens on the first service, but you haven't got all the numbers because you can't be certain what the factory put in...) The difference between the static, normative case and the real-live dynamic case of your bike was breathed out through the seals. Refrain from cleaning your hub for a few months and there will be a slick of thin, relatively clean oil, enough to leave a good deposit on your finger if you rub it across the hub.
This breathed-out oil gets everywhere, including on the circumference of the gear housing between the flanges to which the spokes are attached. Perhaps fancifully, I'm encouraged by the image of my Rohloff gearbox proceeding in a halo of misted oil.