I have an example before me. I have two bottles of Quick, one is chocolate flavoured. On the first bottle, which contains 14 ml, it says 33% less sugar. On the second bottle of Quick, the chocolate one, the serving is 20 ml . So you are comparing a 14 ml portion and a 20 ml portion. On the 14 ml portion, it says 33% less sugar, but that is because it is smaller by 6 ml.
On March 3rd, 2011. See this statement in context.