As stated above, antifreeze can be burned, mixed with you oil, or evaporate from the overflow tank cap pressure regulator. There are also hose leaks that are pinpoint and just enough for a vapor to escape. All said, I would drive it and watch to see if it continues down to the point you see it at the bottom of the overflow... if it makes it down there take it back in, however chances are also that it could even out and stop dropping as stated above, this "self regulating" is due to the overfill cap, which does allow vapor of a certain pressure to escape. Sometimes these caps either go bad or I suppose, could be factory defective.
I own two other VW's (Touaregs) that always read low coolant...a few days after topping off or a year after topping off (same level). For whatever reason, the "minimum" mark on them is too high and if I fill to there it just evaporates. I have no idea why they were designed this way, but I have over 200k miles between them, and they have never overheated. Not even towing our travel trailer in 100 degree heat.