Trappist Trickery

Imagine the box above - purchased from City Super - with a bottle in each of the 3 central slots, and a glass at each end.  The bottles contain one each of the excellent beers brewed by the Trappist monks of Rochefort, one of a handful of Trappist monasteries in Belgium and Holland renowned for their superb strong beers - the rarely seen Number 6, plus the more widely available 8 and 10.

It was only after drinking the beer that I noticed this on the back of the box:

So, where's my extra bottle?